Allison WTECII & WTECIII ECU’s (TCM’s) Power Failure
Troubleshooting Guide
Reference:
https://www.transmissioninstruments.com/troubleshooting/
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Caution!!: The following procedures are technical and should not be attempted if you are unfamiliar with
electronics or uncomfortable working with electrical components. Doing this troubleshooting method is at
your own risk. Although this procedure has been recommended by other Monaco Owners, it should be
used with caution. If in doubt, contact Transmission Instruments
for advice.
Have you recently replaced or charged the battery outside the vehicle? If yes, recheck connections in
your battery compartment and look for two 10 gauge wires. These are near the battery terminals which
supplies positive and negative power directly to your ECU through VIM (Vehicle Interface Module). The
VIM contains two fuses [for ECU only] and up to six relays powered by the ECU (including the start relay).
Recommended Tools :
Light Bulb Type Continuity Tester. Available at many autoparts stores.
Alternative: Assemble 12V/15-25W light bulb (spare brake lamp bulb or similar
– #1156, #1073 etc.) with 20 gauge solid
copper wire (
ordinary hookup or “bell wire”). Strip 1/2″ on test side.
When you check ECU connectors, the lamp must glow bright white light. A dim light will indicate a bad
connection somewhere; likely due to oxidization.
A voltmeter will not indicate bad connections.
An ordinary voltmeter or VOM isn’t reliable for this test.
However you will need one to check the lower voltage systems.
After assembly, check lamp directly on your battery terminals. Caution lamp will become
HOT!
Always disconnect the battery or turn off the battery switch (Power Train Battery) prior to
disconnecting or reconnecting ECU connectors!
