Stranded in transmission full protect mode


My 2003 T1N is stranded in a state carpool parking lot in Saginaw, Michigan, about an hour's drive from my home. The problem arose very suddenly. Leaving a parking lot I felt a small lurch in a low-speed forward gear. About 20 miles of city driving later the engine lost connection to the wheels in 30 mph driving. Power was resumed briefly for a hundred yards or so until a stoplight, where all connection to the wheels was lost.The engine reluctantly starts now and spins in all gears with no forward or reverse movement of the van. Scan with my Autel MD802 yielded the following codes:
P26600 undervoltage
P2500 impermissible transmission ratio
P2502 the gear is implausible or the transmission is slipping
P2200 Speed sensor 2 is faulty.

I gather that the TCM has gone into full self-protect mode. I cleared the codes with the MD802. The codes all disappeared but it did not change the problem at all. I need some serious advice.

1) What is the likely problem and how should I proceed?

2) Is there any way that I can get a quick and dirty repair on site in the parking lot? If I could somehow trick the TCM into at least allowing limp-home mode, I could get the van back into my own driveway and fix it in a less difficult situation. The alternative is a costly flat-bed 60 mile transport.

3) I'm thinking about (a) pulling the drivers seat and checking the TCM for wicking fluid; (b) removing the transmission cover and valve body, bringing them home and checking them out as best I can off the vehicle and perhaps (c) replace conductor plate if indicated. Then drive back, install parts and new ATF and hopefully drive it home, at least in LHM.

I have posted in another thread the question whether the Autel MD802 that I have is sufficient to fully clear all of the codes that I need to clear. If not, is there some secret combination of on-off ignitioin cycles, key fob events and/or accellerator press release sequences to tell the TCM to reset itself or do I need to locate a professional scan unit?

Any help that you folks can offer would be greatly appreciated.


Formerly Type2Teach
First thing you should do is check your transmission fluid. Do you even have any? You will need a special dipstick for this.


Should have mentioned 323000 on van. Did the Doktor A valve body clean and new MB specification ATF 3 years and 50k ago.


Formerly Type2Teach
Also, check the bottom of your transmission pan. Is it wet? Then you are and have been slowly leaking transmission fluid for who-knows-how-long. Chances are that the plug on the front passenger side of transmission pan is leaking at one of its seals. This is very common with your transmission.


Found this in another post. Will it work in my sityation?

Transmission Control Module
In order to ensure a safe driving state and to prevent damage to the automatic transmission, the TCM control module switches to limp-home mode in the event of critical faults. A diagnostic trouble code (DTC) assigned to the fault is stored in memory. All solenoid and regulating valves are thus de-energized.
The net effect is:
· The last engaged gear remains engaged.
· The modulating pressure and shift pressures rise to the maximum levels.
· The torque converter lockup clutch is deactivated.
In order to preserve the operability of the vehicle to some extent, the hydraulic control can be used to engage 2nd gear or reverse using the following procedure:
· Stop the vehicle.
· Move selector lever to "P".
· Switch off engine.
· Wait at least 10 seconds.
· Start engine.
· Move selector lever to D: 2nd gear.
· Move selector lever to R: Reverse gear.
The limp-home function remains active until the DTC is rectified or the stored DTC is erased with the appropriate scan tool. Sporadic faults can be reset via ignition OFF/ON.


Did not see any obvious signs of leakage. The Transmission Plug Wire Harness Connector was replaced 50k ago.


Engineer In Residence
The engine reluctantly starts? What is the voltage when running? Sufficiently low voltage can cause trans limp mode. The tcm power supply has some history of high resistance causing low voltage. You can check the voltage at the tcm using your md802.
Last edited:

Aqua Puttana

Poly - Thread Finder
Found this in another post. Will it work in my situation?
No. Not once the TCM or other module(s) have set the most severe level of LHM. Once that severe mode is locked in a scan tool reset is needed.

The scan tool reset is not a fix, it removes the LHM safety lockouts. If the unwanted conditions remain the transmission will again revert to LHM. Without repairs, a reset may restore operation for a period of time, but that isn't always the situation.


Top Bottom