Allison WTECII & WTECIII ECU’s (TCM’s) Power Failure
Troubleshooting Guide
Reference: https://www.transmissioninstruments.com/troubleshooting/
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Instructions for WTECIII system (single red digit on Your shift selector)
Have you recently replaced battery and accidentally swapped battery terminals?
o If “YES”, ECU may be fried beyond repair.
o If “NOT”, locate the ECU (in most RV’s is near shift selector, close to VIM Module or
mostly on trucks, close to transmission (just follow bundle of wires from
transmission).
o Disconnect the battery first, then unplug all three connectors from ECU and
reconnect battery.
o Closely check the GRAY connector for numbers.
o Insert test lamp leads into corresponding connector sockets: 1 and 32 then 16 and
17.
Next turn “ON” Ignition switch and insert test leads to 17 and 26. If cavity #26 is blank, use
BLACK connector socket #4. Lamp must glow brightly.
#17; #32 = BATTERY GROUND; #1; #16 = BATTERY POWER; #26 gray or #4 black =
IGNITION.
o Next turn ignition and battery “OFF”, reconnect GRAY ECU connector only, then
reconnect battery and turn “ON” ignition.
o Then very carefully touch gold plated pins #16 and #32 (on ECU BLACK connector)
with lamp test leads. Lamp must glow bright.
o Then use a voltmeter to check 5V on pin #3 (on ECU BLACK connector) against
chassis ground. DO NOT use test lamp! If no 5V is found on pin #3, ECU is
defective.
Also check socket #3 on BLACK connector with ohmmeter against chassis ground. Must be
over 4k ohms.
Shift selector can be checked using ordinary 9V battery and hookup wire.
o Connect the 9V battery using hookup wire which you may have to slightly bent on the
ends so they can hold inside BLACK connector sockets.
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