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View Full Version : Is it Possible to Bypass a Sensor to Trick the Computer?


ecowhale
03-26-2017, 04:53 PM
Due to a persistent check engine light even after cleaning my EGR system and sensors (code points to sensor between EGR and catalytic converter), I wish to disable any current sensor tripping the alarm so that I can keep the check engine light off after clearing codes.

Is there a way to rewire a sensor to trick the computer into thinking the sensor is OK rather than spend thousands on a Sprinter tech to replace sensors and parts with the same result?

lindenengineering
03-26-2017, 05:06 PM
Well its begs the question 'whale whether you should fix the root cause or bodge it up!:thinking:

Much better to solve the problem that way than maybe adding to the pollution stack coming out of the tail pipe!

Have you taken it to a decent repair shop for diagnosis or analysis?
Dennis
Mechanic

smiller
03-26-2017, 05:31 PM
If you are talking about an EGT sensor then it is required for proper engine operation so bypassing it is not a very good idea, and they're not that expensive anyway so why not just replace it?

avanti
03-26-2017, 05:54 PM
A lot of the "plausibility" checks the the ECUs perform are dynamic, not static. In these cases, you can't just stick in a resistor.

ecowhale
03-26-2017, 05:57 PM
Not sure which sensor out of about 5 it is; replacing all 5 is around $700 DIY / about $2,000 dealer (200% parts markup and three hours labor).

ecowhale
03-26-2017, 06:00 PM
I'm tired of the dealer here (too unreasonable). I may wait until I go to another area. I didn't want to fix the root if it costs thousands due to this being a 2007 with 170k miles; at that point upon resale, nobody appreciates stellar maintenance.

lindenengineering
03-26-2017, 06:07 PM
Just read my post above about proper maintenance.
Simply because in the end it will do the rig in!
Dennis

ecowhale
03-26-2017, 06:22 PM
Well if I take it to a shop every time a dash warning light comes on, I would rarely get to use it! lol, looking forward to the next generation Sprinter being better quality (what are the chances of that?)

ecowhale
03-26-2017, 06:26 PM
One of my biggest complaints about the Sprinter / stupid German engineering / whoever in charge should be fired or retrained at minimum: Why all these sensors and no temp gauge on the dash??? Makes NO sense at all. Instead, a huge, worthless tachometer.

ecowhale
03-26-2017, 06:31 PM
Linden, I agree despite my replies; I'm just really tired of perpetual dash lights on the Sprinter. Every time I finally get them cleared out, a new one occurs soon after.

lindenengineering
03-26-2017, 06:40 PM
One of my biggest complaints about the Sprinter / stupid German engineering / whoever in charge should be fired or retrained at minimum: Why all these sensors and no temp gauge on the dash??? Makes NO sense at all. Instead, a huge, worthless tachometer.

Well I won't say it stupid . Far from it !
They have different theories about how to achieve the same goal!

In many ways the GMC Duramax in a Savanna van has the same architecture under the engine cover , even down to the exhaust system and the DEF fluid dispensing. BUT that where it ends!

But I know what I prefer and first I am not a midget!
Second the MB engine is fueled in a much more efficient way that the GM product.
Far less special tools and far easier to work on is the MB product !

Like for like repair costs come out cheaper with the MB than the GM product.
Its good to compare.
Dennis

autostaretx
03-26-2017, 06:48 PM
Since you don't know (or aren't saying) which sensor is at fault, it's really hard to answer your question accurately.

Here's the "how it works" section for the Oxygen sensor (which is what is used to plan EGR operation) for the T1N model years.
But it may be directly applicable to your 2007.
Reading through the description, your ECU may be satisfied ("everything's OK":thumbup:) if you replaced the sensor with an ever-so-slightly-less-that-450 millivolts source. (per top of third image)
((you could also measure your current O2 sensor's output, to see if it's speaking reasonable levels))

84294

84295

84296

84299


The T1N's connection diagram and a shorter "how it works" is in this extract from the 2006 service manual: 84298

If you try it, tell us if it works... (although the ECU may get upset if it doesn't see the load of the Oxy Sensor's internal heater)
((looking at the diagrams (again), i see there is a "pump current" feedback channel, as well... that probably supplies the "open circuit" and "short circuit" detection, as well))
--dick
p.s. of all of the Sprinter's complex systems, i consider the O2 sensor ionic-flow operation as being the closest to "magic"

p.p.s. plodding thru a 2007 diesel wiring diagram, i see you've got an exhaust pressure sensor, plus two or three temperature sensors... jeesh...

showkey
03-26-2017, 06:58 PM
Not sure which sensor out of about 5 it is; replacing all 5 is around $700 DIY / about $2,000 dealer (200% parts markup and three hours labor).


We talked about this in another post.........depending on your scan tool ( code reader) your getting an EGR code ? But as you discovered there are multiple sensors and parts like the EGR valve, two temp sensors, EGR pressure sensor, cooler etc etc .

A MB friendly scan tool ( code reader) will tell you which component is likely at fault. This is not absolute, it does take skills and experience to interpret any scan tool data. These skills and experience requirements are not just MB all vehicles have these requirements when Troubleshooting.

Like it or not most scan tools do not "talk" MB at least not to the level needed to fix the problem. This is best proved by the scan gauge, great for reading live data while driving, not so good in code reading.

autostaretx
03-26-2017, 07:27 PM
The exhaust gas temperature sensors are highly likely (almost guaranteed) to be twisted-wire thermocouples... they may even be interchangeable (i didn't look up the part numbers).
Thermocouples are voltage-generators... the twisted wires themselves pump out a tiny voltage (zero to 50 millivolts?) in response to being heated. They're pretty bomb-proof below 1500 F.

You may also be facing an underlying problem of a "common mode failure"... a broken copper trace inside the ECU in the circuit that supplies the reference "ground" to the sensors.

--dick

ecowhale
03-26-2017, 07:40 PM
The Sprinter does cause a lot of unnecessary stress when it shows a dash light, particularly engine light that could be a hundred different things and no temperature gauge making me always wonder how hot the engine is. About 40% of the entire instrument cluster is taken up by a useless tachometer... very annoying.

Cheyenne
03-26-2017, 07:48 PM
The Sprinter does cause a lot of unnecessary stress...

and no temperature gauge making me always wonder how hot the engine is.



Get a ScanGauge II or UltraGauge and you can monitor ECT (Engine Coolant Temp) to the nearest degree (F or C).

I run a SG II in my T1N as I'm sure do a lot of other owners.

PS They also give you a lot of other useful info.

Keith.

autostaretx
03-26-2017, 08:03 PM
Some of the inexpensive scanners (like the UltraGauge (i think) ((and maybe the ScanGauge))) can also report EGT "live".
I'd have to look at the manuals, but they may also be able to report the Oxygen Sensor's output, too...

--dick

dodger413
03-26-2017, 09:32 PM
the holy grail of Sprinter ownership............a switch to turn OFF CEL lights

Sprinter ownership doesn't allow CEL-ophobia !! they are merely suggestions.

keep driving with all sorts of lights on till the thing won't run anymore. THEN the problem MUST be diagnosed !!

ecowhale
03-26-2017, 10:34 PM
lol, cute

ecowhale
03-26-2017, 10:37 PM
Scanner code is: P040D $7E8 Generic Exhaust Gas Recirculation Temperature Sensor A Circuit High

Anyone know exactly where that sensor is? I cleaned the EGR and the sensor next to it.

autostaretx
03-26-2017, 11:14 PM
Scanner code is: P040D $7E8 Generic Exhaust Gas Recirculation Temperature Sensor A Circuit High
Ya know? It would've really really helped if you'd said that in the first place....

Since i don't have detailed 2007 documentation, i'm guessing that that sensor only sees "typical engine block" temperatures (mitigated by coolant).

added: ...and that guess is very very wrong (see Dennis' post far below)

That would give us this curve:

84325

(that's the curve for the 2006's coolant and fuel temperature sensors)

So you could replace it with a resistor ... or, perhaps better, a potentiometer (variable resistor/volume control) which would let you change its "reading" as seen by the ECU.

You could start by simply measuring the sensor's resistance now, with the engine off.
Compare your reading to the ambient temperature's theoretical resistance.
68 F should be about 3000 ohms, cooler is higher.
If at 68F or below you're seeing a resistance of less than 1000 ohms, that sensor is bad.
(i went through three IAT sensors ... once per year... at 68F the last bad one was 600 ohms)

Anyone know exactly where that sensor is? I cleaned the EGR and the sensor next to it.
My 2007 wiring diagram merely says "on engine".
The colors of the two wires going to it are:
Pin 1: Yellow with a dark blue stripe
Pin 2: dark green with a yellow stripe

Pin 2 goes to "sensor ground" at the ECU (so it should be a zero volts... if it's higher, the wire is broken)
Pin 1 is the sensed resistance ("sensor signal")

--dick
p.s. my IAT sensor came out of the engine reading less than 100 ohms at 68 F. Aggressive "cleaning" got it up to the 600 ohms reported above. (and the IAT be 6000 ohms at 68F)
Here's the 2006 IAT page, so you can see the circuit that drives one of these, plus that higher-resistance sensor's curve. Which one (3000 ohm or 6000 ohm at 68F) you have still wants to be above 1000 ohms at 100F

84326

ecowhale
03-26-2017, 11:47 PM
The code is due to engine / coolant overheating and not exhaust?

autostaretx
03-26-2017, 11:50 PM
Anyone know exactly where that sensor is? I cleaned the EGR and the sensor next to it.

The red-circled item is theoretically it. (assuming you have a OM642 engine)

84328

--dick

lindenengineering
03-26-2017, 11:55 PM
Guys let me post this as a semi tutorial.
This guy has an EGR cooler problem but he doesn't want to spend a dealer fee to correct the issue !

OK let's see what's is going on!
If you look over the engine under the hood you can see the cooler . Its a well made compact unit in S/S. Feeding it is a tube coming directly straight off the turbo Y pipe, It enters the cooler via an end cover underside where sits a spring loaded vacuum cylinder and a sensor called the exhaust back pressure sensor.

So this spring loaded vacuum cylinder is actually holding an internal gate flapper closed so that the majority of the exhaust gases do not flow continually throughout the cooler.
So first thing to test to see if it springs back and doesn't stick! Is there sufficient vacuum to the little poppet electrical valve just above it. That vacuum valve is connected to a tee at the servo assy and then to the vacuum pump! Is that plastic piping in good shape?

You can test it all with a hand vacuum pump!
OK as with this originator the cooler is partially plugged if not almost stopped up!

So when the PCM control commands EGR flow the flapper valve opens and in rushes the very hot gases often in excess of 1000 degrees F
If the cooler is restricted, the end velocity of the incoming hot gases literally blasts the EGR valve and the sensors at either end that are telling the PCM how long they are to be held open for!
Obviously the more choked up they are the longer the gas blast punishment continues!
That gas of course enters the inlet manifolding with a strong chance of carbonizing the intake oily deposit and you get early EKAS sticking, elevated upper cylinder temperatures and piston coking!

If left to continue!
With all this gas basting about is it any wonder that the EGR valve itself starts to stick & not perform to spec! Result??
Everyone goes cleaning EGR valves, (having left the marital bed on Sunday morning) unpicking them etc etc when in fact in most cases the valve has been rendered as junk due to neglect and not wanting to fix the root cause of the problem. Of course if the valve is partially stuck open some exhaust gases will be fed into the engine when driving under load!

Can you all see why proper maintenance of the system is essential for engine longevity?
To Recap
The EGR is there to put the fire out and control NOx production!
If you don't cool the EGR exhaust gas transfer you will cook the engine internals and it will kill the engine if left long enough! Should I mention:-This accelerates coking conditions in the engine.
Now ask me about why NOx sensors are failing with a fault code or are they ????
Dennis
Mechanic

autostaretx
03-27-2017, 12:17 AM
The code is due to engine / coolant overheating and not exhaust?
Since you're not reporting other codes, nor symptoms such as "starts grass fires if parked on lawn" or "fries squirrels who run underneath Sprinter" ... i'm going on the simplest explanation: bad sensor.

BUT .. if it were me, i would do as i've already written: MEASURE the CURRENT SENSOR's resistance, dammit.

Engine off.
If it's really an "exhaust" sensor, it'll be a thermocouple (and i'd have to go look up what a thermocouple looks like to an ohmmeter.. it may be near zero resistance... or infinite).

If it's really a coolant sensor, it would be somewhere in the 6000 to 3000 ohm range (if good).

The code is only the first step on the path to diagnosis.
If you're not telling us the OTHER codes that you're seeing, we'll spend another 8 hours making bad guesses and barking up wrong trees (assuming the squirrel didn't get fried)

--dick
(added: above posted before i saw Dennis' reply. Believe Dennis!)
p.s. i am far more familiar with the T1N's OM647 systems... and our EGR is water-cooled. Hence my guesses about the temperatures involved. Upon re-reading the service manual's 647's EGR section, i see that the T1N's operates at 600F (after two cooling stages), so the "3000 ohm" thermistor would be inappropriate for us, too... but we don't have a separate EGR temperature sensor, it's probably buried in the EGR's motor driver module.

Tooth Fairy
03-27-2017, 08:09 AM
Now ask me about why NOx sensors are failing

Dennis, no news to you, you are a f*cking legend. :rad:

vnvet
03-27-2017, 04:04 PM
I'm tired of the dealer here (too unreasonable). I may wait until I go to another area. I didn't want to fix the root if it costs thousands due to this being a 2007 with 170k miles; at that point upon resale, nobody appreciates stellar maintenance.

After reading this, https://www.linkedin.com/pulse/fatal-flaw-mercedes-benz-sprinters-tom-robertson

one might not want to ever own one. As for myself, mine was a daily 200 mile RT freeway driver that has 3-1/2 pages of dealer maintenance and repair records done by previous fleet owner and the MPH set to 65. I'm told by MB mechs., I probably got a good one since it had so much done to it every 10,000 or sooner. I love driving it, gets 19+mpg and hope I can get it to 400k without causing bankruptcy. I paid 18K, so far I've put 2600.00 into it (tires, brakes, struts, shocks, re-tune/update, oil change, trans service & fuel filter).

Good luck with yours.

lindenengineering
03-28-2017, 01:41 AM
I posted ARRIBA!
Yeh lads up thur!

Now ask me about why NOx sensors are failing with a fault code or are they ????
Dennis

This is important because if you are blasting the intake system & combustion chambers with super heated exhaust gases via the EGR and remixing it in the Cat and DPF something has got to melt!
The NOx sensors maybe?

Your indication of something wrong is a NOx sensor malfunction code often affecting the rear unit!
Would you like me to give you some case samples?
Dennis

Bobnoxious
03-28-2017, 02:55 AM
Well if I take it to a shop every time a dash warning light comes on, I would rarely get to use it! lol, looking forward to the next generation Sprinter being better quality (what are the chances of that?)

Say what?:lol::lol::lol:

Bobnoxious
03-28-2017, 02:56 AM
Put tape over the CEL?

Bobnoxious
03-28-2017, 03:02 AM
the holy grail of Sprinter ownership............a switch to turn OFF CEL lights

Sprinter ownership doesn't allow CEL-ophobia !! they are merely suggestions.

keep driving with all sorts of lights on till the thing won't run anymore. THEN the problem MUST be diagnosed !!

Or until LHM.

ecowhale
03-28-2017, 11:33 PM
The male thread section on the cooler broke off when I tried to remove it. I cleaned the sensor with brake cleaner and re-installed via JB Weld, but have same code problem; therefore I'll buy a new sensor and install again with JB Weld to hold it on (cost of new cooler and down time not something I'm willing to entertain). Any thoughts of doing that?

ecowhale
03-28-2017, 11:38 PM
More info that may help diagnose: The check engine light comes back on very quickly after clearing the code (same code) even when engine "not very hot". To me this sounds like a bad sensor.

OrioN
03-29-2017, 12:06 AM
:popcorn:













.

ecowhale
03-29-2017, 12:37 AM
Orion... your last message is empty (?)

Bobnoxious
03-29-2017, 01:44 AM
Orion... your last message is empty (?)


I'll pass on that set up.

ecowhale
03-29-2017, 02:46 AM
The red-circled item is theoretically it. (assuming you have a OM642 engine)

84328

--dick

Thanks, Dick, most helpful post (and image) yet.

ecowhale
03-29-2017, 02:48 AM
Guys let me post this as a semi tutorial.
This guy has an EGR cooler problem but he doesn't want to spend a dealer fee to correct the issue !

OK let's see what's is going on!
If you look over the engine under the hood you can see the cooler . Its a well made compact unit in S/S.
Dennis
Mechanic

I disagree because the male threaded part the sensor connects to very easily broke off due to cheap steel and bad design (hollow center / thin wall).

The rest of the message could prove very useful and will check it out further for diagnosing.

ecowhale
03-29-2017, 03:15 AM
I'll pass on that set up.

Before you make that your final decision, consider: At least I didn't use duct tape :lol:

Actually JB Weld is not much worse than the German engineered thin wall threads that break.

Bobnoxious
03-29-2017, 03:37 AM
Thanks for being a good sport! Wish I could be more helpful! JB Weld has its uses. I hope you resolve your issue. In reference to "passing on the set up" I was going to say that most of Orion's messages are blank.

morre
03-29-2017, 05:08 AM
heres my answer to OP's question, YES it is Possible to Bypass a Sensor to Trick the Computer, and specially such a useless sensor as egr temp.

ecowhale
03-29-2017, 05:19 AM
heres my answer to OP's question, YES it is Possible to Bypass a Sensor to Trick the Computer, and specially such a useless sensor as egr temp.

Please tell me how asap... just placed order for one on eBay for $100 may not be too late to cancel... (I know that's a chunk of change just for one troubleshooting step, but way far less than dealer diags and parts, sensor of which I'm sure they would charge double for)

OrioN
03-29-2017, 06:24 AM
:popcorn:










.

morre
03-29-2017, 03:28 PM
of course if we talking about EGR temp sensor not a EGT sensor.
find any local tuner and ask to do EGR delete and intake flap delete, it will cost more then sensor replacement but in a long run it will be cheaper.



Please tell me how asap... just placed order for one on eBay for $100 may not be too late to cancel... (I know that's a chunk of change just for one troubleshooting step, but way far less than dealer diags and parts, sensor of which I'm sure they would charge double for)

avanti
03-29-2017, 03:36 PM
of course if we talking about EGR temp sensor not a EGT sensor.
find any local tuner and ask to do EGR delete and intake flap delete, it will cost more then sensor replacement but in a long run it will be cheaper.

...and it is against the law.

lindenengineering
03-29-2017, 03:47 PM
Just a question??
What does the EGR valve do?

Does it merely allow a recirc of exhaust gas to put the fire out?
Does it facilitate a re-gen activity?
Does it do anything else? Like maybe an aid to fuel consumption reduction on light cruise?
Dennis
Mechanic

morre
03-29-2017, 03:50 PM
"...and it is against the law"

sure it is, question was "is it possible" answer "yes it is", OP didnt ask "is it legal to bypass sensor"

lindenengineering
03-29-2017, 04:03 PM
If it is a deliberate act to disable a Federally mandated emissions device!!!!!!
Then yes it is.
Dennis

Bobnoxious
03-29-2017, 05:25 PM
I know it sounds corny but following the "rule of law" is the cornerstone of excellent citizenship. Needless to say emission controls are enacted to protect the air "we all breathe." Now if sanctuary cities would follow federal law our cities would be safer.

Everyone's skill-set, time, and financial circumstances vary widely. My suggestion, as a fellow Sprinter owner, is if you plan on being a Sprinter owner become as familiar with your vehicle as possible because she's a quirky beast she is! No person is going to exercise the same care when maintaining your vehicle. Mercedes-Benz dealerships do not necessarily equate to repair/service excellence. One small example. Oil changes. I am meticulous about not spilling a drop of oil, even while removing the dipstick, any where on the vehicle. Spilled oil, of any quantity, will spread out, collect dirt and bake on the engine tighter than nuts on a new bridge, look like hell and make a greasy mess if you have to effect repairs.

Eventually, when I am certain it will cover my model year, I'm going to purchase a Xentry diagnostic clone and suggest the same. Ben Johnson in the "Scanner" area is blazing the trail for us providing priceless info.

Good luck, I wish you well!!

ecowhale
03-30-2017, 12:23 AM
of course if we talking about EGR temp sensor not a EGT sensor.
find any local tuner and ask to do EGR delete and intake flap delete, it will cost more then sensor replacement but in a long run it will be cheaper.

Would that still require the sensor though to prevent check engine light?

morre
03-30-2017, 02:36 AM
no need for sensor if its done right.

software can be modified and any error can be removed from memory of engine control module.

Would that still require the sensor though to prevent check engine light?

ecowhale
03-30-2017, 03:18 AM
no need for sensor if its done right.

software can be modified and any error can be removed from memory of engine control module.

Where can I get instructions or find someone capable?

morre
03-30-2017, 03:49 AM
anywhere in a world any local tuner should be able help you, anybody who does chip tuning for BMW or VW or Mercedes. sprinter uses same ECU like any other car manufacture in a world, just different software. for example EDC16 ecu can be found in a sprinter and every other manufacture including Japanese and Korean brands.
or you can use remote tuner like GDE, Malone or any other company. if your truck '10 or newer you'll have to ship you engine control module to them.

you'll tell them what need to be done such as: egr delete, intake flap delete, DPF delete, Adblue delete, DTC delete(provide list of dtc's), hot start fix, Immo delete(03 and older sprinter), performance tune, hot tune. or any other requirement.
you can even have "OBD readiness monitors" set and they will stay set forever.

if you have any hardware modifications done like bigger turbo, straight exhaust, bigger injectors, proved a list to tuner so it all can be taken in account, of course nobody does any hardware modifications for sprinter.

ecowhale
03-30-2017, 03:54 AM
OK, thanks; if I go to resell and the next owner finds out what I did, can that come back on me somehow? I would feel better to have the new owner sign an "AS IS" waiver, but not sure that would insulate me from trouble with the government, but that seems very unlikely especially with Trump's cronies over the EPA.

morre
03-30-2017, 04:22 AM
new owner will only thank you for that.

you can always return it to stock, if needed, tuner will save your original software before modifying it. if your truck 07-09 you can get little portable device(like one provided by GDE and made by alientech) where you can have both files saved, and you can change it on a fly, 5 min job. only problem with this device it gets married to only one vehicle.

also any software update from dealer will remove your modified file and will bring it back to stock.

Brokecanadian
03-31-2017, 05:36 AM
Why do I get the feeling the only sprinter mechanic here is being ignored?

SprinterHelp
03-31-2017, 10:16 PM
Its not German Engineering, its our stupid EPA and the low quality fuels and oils they sell us. Go into the auto parts store and almost all the oils are mid quality. All the manufacturers have a top line or top shelf oils which they WILL NOT SELL.

ecowhale
03-31-2017, 10:51 PM
Its not German Engineering, its our stupid EPA and the low quality fuels and oils they sell us. Go into the auto parts store and almost all the oils are mid quality. All the manufacturers have a top line or top shelf oils which they WILL NOT SELL.

True regarding the fluids and oils, but the male threaded part that broke is indeed poor engineering.

Bobnoxious
03-31-2017, 11:55 PM
Its not German Engineering, its our stupid EPA and the low quality fuels and oils they sell us. Go into the auto parts store and almost all the oils are mid quality. All the manufacturers have a top line or top shelf oils which they WILL NOT SELL.

Where, may I ask, can I purchase said top-shelf oil? Christina, mein Sprinter demands the best. If she has any inkling I am short changing her, they'll be hell to pay! (Checking spec) or equivalent manufacturers specification 2015?

ecowhale
04-01-2017, 04:10 AM
Where, may I ask, can I purchase said top-shelf oil? Christina, mein Sprinter demands the best. If she has any inkling I am short changing her, they'll be hell to pay! (Checking spec) or equivalent manufacturers specification 2015?

You can get Mobile 1 ESP 5-30 at Pep Boys for about $11 per quart. About 10% of O'Reileys might have it for around $12 per quart.