L322 5HP24 Low Voltage ECU

Hi, Looking for some technical advice please ?
I have a 55 L322 TD6 with 5HP24 Gearbox.
Gearbox fault on dash is Std Trans Safe Mode, but only drives forward in 3rd.
No Reverse, but you can feel it go in and load the engine, but must be being held by a brake.
Every time I Read Codes for Gearbox or transfer box the codes are different or at least inconsistent.
Generally can bus comms faults and speed sensors but not the same speed sensors.

Vehicle has a new Battery and alternator checked.

overview of the Gearbox with diagnostics shows the gearbox ECU Voltage at 9V or 11V with engine running. Engine ECU Voltage through Diagnostics is Normal 12 and 14V.
I have measured 3 + and Check 3 Grounds at the ECU module and Voltages are all normal.

So !!, Where should I be looking if the ECU itself gives diagnostic data at low voltage and I also have various Can Bus Faults but inconsistent which must be related to low voltage ??

Much Appreciated

Mark

hottrader2000 said:

I have a 55 L322 TD6 with 5HP24 Gearbox.

Click to expand...

Err, no you haven’t.



If you temporarily disconnect the 20-pin connector at the back of the transmission this will force the transmission into mechanical/hydraulic failsafe which is totally independent of the electronics & ECU. You should be able to select reverse and move backwards as usual. If you can’t, then you have a mechanical or hydraulic issue which has nothing to do with the ECU.

Phil

Bemble said:

Err, no you haven’t.

If you temporarily disconnect the 20-pin connector at the back of the transmission this will force the transmission into mechanical/hydraulic failsafe which is totally independent of the electronics & ECU. You should be able to select reverse and move backwards as usual. If you can’t, then you have a mechanical or hydraulic issue which has nothing to do with the ECU.

Phil

Click to expand...

I stand corrected ! It is the GM box.

Today we removed the sump, tested speed sensors, tested solenoids. Nothing major to report in the box, looks immaculate.

When In drive its only in a fixed gear and the first codes up are speed monitor 1 & 2.
No reverse, but it does load the engine, just doesn’t move.
In neutral it will roll forward, but won’t roll backwards.

With snap on verus, engine ecu voltage is 13.8, same in transfer box ecu and abs ecu. But gearbox ecu is only 11.2v.

Snapon also shows gear selector invalid state, but no fault code related. Dash shows P,R,D correctly.
Low range and transfer box operate ok with no codes.

so.... thanks for the reply. Tomorrow we I’ll disconnect the loom feed to the box and try again.

Phil,

Really appreciate your input.
I’ll update after testing tomorrow.
Mark