Copyright © 1998 General Motors Corp. 6–119
WTEC II ELECTRONIC CONTROLS TROUBLESHOOTING MANUAL
Main code 66 indicates the ECU is expecting to get its throttle position sensor (TPS) signal across a serial
communication interface from a computer-controlled engine. Either the engine computer is not sending the TPS
information or the wiring between the engine and transmission computers has failed.
Code 66 00 can occur when the transmission ECU remains powered when the engine ECM is powered down.
The transmission sees this as a communication link failure.
NOTE: If a Code 66 00 is set and the ECU was programmed after 9/26/94, the SERVICE icon on the shift
selector will be illuminated.
Active Indicator Clearing Procedure:
• Power down
• Manual
• Self-clearing
Troubleshooting:
1. Check for a TPS signal from the engine to the transmission, an engine computer malfunction, or an
engine TPS fault.
NOTE: Throttle position data sent from a computer-controlled engine will not register counts on the DDR.
2. Check wires 142 and 151 between the engine and transmission ECUs, for an open or short, and
check that all connectors are clean and tightly connected.
3. Use the Pro-Link
®
to see if the ECU is receiving power when it should not.
CODE 66 XX — SCI (SERIAL COMMUNICATION INTERFACE) FAULT
(Figure 6–40)
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