'98 ML320 won't shift out of 1st gear
 

Out of the blue our ML320 has decided not to shift out of 1st gear. It will drive around just fine in 1st gear, but we can't go anywhere obviously. The ABS, ETS lights are on.

The code reader showed codes for the brakelight switch, which I replaced today and there are 2 codes related to the rpm sensor:
C1100 Rpm Sensor FL
C1100-016 Rpm Sensor discontinuity

Also, when trying to access the ME2-SF1 Motor Electronics heading on the scanner the tool reads, "Fault in communication with ECU."

When first hooking up the scanner it "hints" at the Electronic Selector Module.

This transmission has always driven great. There are 200K miles on it, but it was always serviced and flushed a year ago, refilling with new fluid. I have a feeling there is something other than the tranny preventing this thing from driving.

Any ideas? Is the Rpm Sensor located within the conductor plate? I know there are 2 sensors inside of the conductor plate, but I don't remember what 2. Maybe transmission speed sensor and Rpm sensor?

Any help would be greatly appreciated. Thank you!

Can you get live data through your scan tool? There is a front and rear RPM sensor in the conductor plate so reading that would be helpful.

The 722.6 trans you have actually defaults to 2nd gear so you would be able to get a bit more speed up than just 1st.

I have experienced this a few times. The transmission actually stays in first gear in such failure if the mode select switch was left in S. The identifier of this failure is that your gauges will not show the gear position. Its quite odd I know, because the failure is intermittent the TCU does recognize the shifter select once and allows the 1st gear shift to be initialized. Then it goes blind and stops.

This can happen from a very low battery or a faulty gear select lever unit too - In my case the car I was working on was the same as yours and the gear selector was indeed faulty, You need to connect your scan tool and test the EGS module for gear position.

a bit more info is that it showed up on very hot days.

2nd gear is 'Default" . Does Reverse work ?

A live scan will id a fault but external problems are not unknown. By the front passengers side of the transmission is the TCM to trans' loom of 14(?) wires. They are covered by a small shield as they leave the transmission.

This loom is routed up to the body very close to the primary cat' in the down pipe exhaust. The possibility of this bundle of wires being cooked is very high.

Remove the loom shield and cut away the loom sheath. tease out all the wires and look for insulation melting and deterioration allowing wires to short together.

You can buy a new loom or carefully insulate each wire. If there is a lot of pink ATF leaking from the transmission multi pin plug, there is a kit of parts to reseal it.

There are some 'How To's' on You Tube showing the procedure and eBay etc has Conductor Plates if it turns out the relay board is bad.

I hear some say the ATF can wick into to TCM causing it to fail, but if you think about this for a minute, it seems unlikely. The Conductor Plate relays and sensors in the transmission do fine submerged in ATF and some transmissions have the TCM inside the transmission.




.

Plain oil in the TCU wouldn't be a problem. This issue is graphite from clutches / suspended metal in the oil is conductive and can cause problems at the TCU because much of it runs at very low voltage. Any stray voltage across traces can cause a problem.

So....what the hell was the problem ? :mad:



.