Desperate Limp Mode Help

Srwilliams · Srwilliams's Garage

My 2003 325ci has gone into limp mode (running only in 4th gear) with the service check light on.

I took it to have checked out and it was diagnosed that full power was not being transmitted from the ECU power supply to the transmission. I was told I would have to do a "Pin Test" on all of the wires , that is to unhook all of the wires from the ECU and test each wire independendently to find the bad wire. If not a bad wire then I have a bad ECU. This is what a shop told me as a start point guess.

Can you guys point me in the right direction. Does this sound about right. Any other suggestions.

Also, can anyone point me in the right direction on how to do this pin test and where can I get an illustration of the wires going from the ecu to the tranny that could possibly be bad so I can trace them

Any help would be greatly appreciated.

AGI · 04-10-2009, 01:23 AM

OK, let's get things straight. Why should a wire go heywire? Have you left the car at a bodyshop for a while to mend it after an accident. Have you recently been fitting any after market phones, Hi-Fi systems, etc? Have you had a part replaced such as an evaporator, etc?

If none of these have been performed lately, then a wire shouldn't just get cut left to its own devices. BMW cables, bus systems are super high quality stuff. Also, keep in mind that all shops blame a unit controlling the mechanical part at the time of a malfunction. Not necessarily.

Your EGS unit is in close touch with your DME (engine ECU) making sure full torque is not applied to the gearbox at the time of a gearchange, monitoring the position of your gear lever, etc, etc.

It is possible in this case for the EGS to have gone out to lunch. Two tests you may do:

1) Get your instrument cluster out and take both plugs off (the black one and the white one) and see if your box is acting any different.

2) Try this with an identical EGS. You do not need a carbon copy of your car. You may try it with the EGS of a 320, 325, or a 330. If you can get hold of a car as such, let me know and I'll guide you further!