Powertrain Controls - ECM/PCM

Code 61 Diagnostic Chart:

Cruise Servo Circuit Diagram:

CIRCUIT DESCRIPTION:
The cruise switch within the turn signal lever receives ignition voltage from a 15 amp fuse through CKT 639 to the turn signal lever cruise switches. The cruise on/off, set/coast, and resume/accel switches are inputs to the cruise control portion of the PCM.
The cruise servo vent and vac solenoids are the output lines and are controlled by high side drivers in the PCM (in this case, the circuit is grounded on one side and the "high side drivers" in the PCM provide power.) When the ignition is "ON", the PCM looks at these output lines and will set codes depending on the status of each line.

OPERATION
The vent solenoid is a normally open (de-energized) solenoid that vents the cruise servo to the atmosphere, preventing any vacuum from being applied. When the solenoid is energized ("ON"), the vent is closed and the cruise servo holds vacuum, allowing the servo to retract and open the throttle.

Code 61 will set if:

^ A short to voltage on CKT 403 occurs, energizing the solenoid when the PCM is commanding the solenoid "OFF" (de-energized).
^ CKT 403 is open.
^ CKT 403 is shorted to ground when the PCM is commanding the vent solenoid "ON".
^ One of the above conditions are met for more than 0.5 seconds.

NOTE: Code 61 does not turn on the "SES" light.

DIAGNOSTIC AIDS:
An intermittent may be caused by a poor connection, worn through wire insulation, or a wire broken inside the insulation. Check for:

^ Poor connection or damaged harness. Inspect harness connectors for backed out terminals, improper mating, broken locks, bad terminals, poor terminal to wire connections, and damaged harness.