Powertrain Controls - ECM/PCM

DTC 31 Engine Speed Control Governor Chart:

DTC 31 Engine Speed Control Governor Circuit:

CIRCUIT DESCRIPTION:
The Powertrain Control Module (PCM) sends a pulse width modulated signal to the engine speed control governor module (CKT 934) to drive the D.C. engine speed control governor motor.
Depending on the amount of governing required, the module translates the PCM data into the appropriate value of D.C. current (CKTs 932, 933) to the motor, which pulls back the throttle to correct the overspeed condition. Note that the system is capable of holding the throttle at an idle (100% authority).
The PCM control of the engine speed control governor module is based on Engine Speed (RPM).

DTC 31 WILL SET WHEN:
^ PCM is commanding near 100% authority.
^ Engine RPM is higher than calibrated governed speed.
A DTC 31 will detect a faulty PCM, engine speed control governor module, motor, linkage or wiring. If DTC 31 is set, the PCM will limit engine and vehicle speed by momentarily reducing fuel.

DTC CHART TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Determines if engine speed control governor module has supply voltage with which to operate.
2. Applying + 12 volts to the motor will determine motor, wiring, and linkage integrity. DO NOT hold current to the motor for longer than 30 seconds, as damage to the motor could result.
3. This will command 100% (full) governing, to determine if the PCM or the engine speed governor control is at fault.

DIAGNOSTIC AIDS:
Before replacing PCM, use ohmmeter and check resistance of each PCM controlled relay and solenoid coil.
For coil terminal identification of solenoid(s) and relay(s) to be checked, refer to PCM wiring diagram in ENGINE CONTROL MODULE/DIAGRAMS/ECM/PCM WIRING DIAGRAMS.
Electrical Diagrams
Replace any relay or solenoid where the coil resistance measures less than 20 ohms.
Refer to DIAGNOSIS BY SYMPTOM/INTERMITTENTS.
- Intermittent Malfunctions