DTC U0101, No Engine Crank and No Tech II Communication with TCM - keywords control engage mil LCT1000 mw7

This PI was superceded to remove break out box test procedure and add model years. Please discard PIP3605.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Customer may comment that the vehicle will not crank to start or will not shift, after the vehicle has been jump started due to battery run down or after installation of after-market equipment. Technicians may find no communication with the TCM and or DTC u0101 stored in other modules.

A few TCMs have been returned from the field for analysis because of the above symptoms. The field returned TCMs mentioned above were analyzed and found to have two battery ground nodes inside the TCM damaged by excessive electrical current passing through the heatsink of the TCM. The nodes affected, described as wire-bonds, are tied to pins 9 and 69 (battery ground pins) of the TCM.

The TCM is manufactured so that the heatsink of the TCM is electrically isolated from all vehicle electrical systems including vehicle chassis ground. Do not ground welders, battery chargers, electrostatic painting equipment or any other electrical devices to the heatsink. Disconnect the 80-way connector from the TCM when electrically welding on the vehicle.

To avoid damaging a TCM in this manner, NEVER ALLOW the following:

1. Battery positive wires to touch the heat-sink of the TCM (e.g. when jump-starting vehicle).
2. Positive battery power chassis harness wire to pin 10 and pin 70 of the TCM to be wired without fuse protection of 10-15 amp.
3. Physical contact between heatsink and vehicle chassis or other circuit ground points.
4. Electrical grounding of devices such as arc welders, battery charger cables, electrostatic painting equipment, or jumper cables to the TCM heatsink.

Take the following steps to check for damaged ground wire bonds if the symptoms for a concern are "No engine crank" and/or "No communication" with Tech II.

1. Switch ignition key off.
2. Disconnect the TCM electrical connector and remove TCM from the vehicle.
3. Test for continuity between pins 9 and 69 at the TCM. If continuity exists between pin 9 and 69, then refer to steps in eSI for "No engine crank" and/or "No communication".

If the circuit between pins 9 and 69 have no continuity, then the TCM has been damaged from some external source shorting to the heatsink of the TCM.

1. Inspect for the source that shorted to the TCM heatsink.
2. Eliminate or repair the source or condition that caused the damage.
3. Replace damaged TCM after the condition that caused the TCM damage has been corrected.

Note:  Visual surface pits and carbon deposits are typically found on the TCM heatsink when high energy arcs are generated by shorts between the heatsink and battery power.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.