Programmable Speedometer/Odometer Module (PSOM)

1994 PCED OBDI-A

SECTION 6A: EEC-IV Pinpoint Test
Procedures

DS: Programmable Speedometer/Odometer Module (PSOM)

DS1 DIAGNOSTIC TROUBLE CODES (DTCS) 29 AND 452: CHECK PSOM RESISTANCE

Continuous Memory DTC 29 indicates that during the last 80 warm-up cycles, the PCM detected an error in the PSOM output signal. DTC 452 indicates the PCM detected an error in the PSOM output signal during the last 40 warm-up cycles.

Possible Causes:

Damaged Rear Anti-Lock Brake System (RABS).
Damaged PSOM.
Damaged harness circuits.
Damaged PCM.

Key off.
Disconnect Powertrain Control Module (PCM). Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box, leave PCM disconnected.
Measure resistance between Test Pin 3 and Test Pin 6 at the breakout box.

Is resistance between 21,000 and 55,000 ohms?

Yes	No
GO to DS4.	GO to DS2.

DS2 CHECK CONTINUITY OF THE HARNESS CIRCUITS

Key off.
Breakout box installed, PCM disconnected.
Disconnect PSOM.
Measure resistance between Test Pin 3 at the breakout box and PSOM(+) circuit at the PSOM vehicle harness connector.
Measure resistance between Test Pin 6 at the breakout box and PSOM(-) circuit at the PSOM vehicle harness connector.

Is each resistance less than 5.0 ohms?

Yes	No
GO to DS3.	SERVICE open circuit. REMOVE breakout box. RECONNECT all components. RERUN Quick Test.

DS3 CHECK HARNESS CIRCUITS FOR SHORTS TO POWER AND GROUND

Key off.
Breakout box installed, PCM disconnected.
PSOM disconnected.
Measure resistance between Test Pin 3 and Test Pins 6, 37 and 40 at the breakout box.

Is each resistance greater than 10,000 ohms?

Yes	No
GO to DS4.	SERVICE short circuit. REMOVE breakout box. RECONNECT all components. RERUN Quick Test.

DS4 CHECK RABS SENSOR RESISTANCE

Key off.
RABS disconnected.
Measure the resistance of the RABS.

Is resistance between 1300 and 1550 ohms?

Yes	No
GO to DS5.	REPLACE the RABS. REMOVE breakout box. RECONNECT all components. RERUN Quick Test.

DS5 CHECK PSOM OUTPUT VOLTAGE

WARNING: THIS TEST STEP REQUIRES ANOTHER PERSON TO ACCOMPANY THE DRIVER TO MAKE MEASUREMENTS AND RECORD DATA. ALL APPLICABLE SAFETY PROCEDURES AND TRAFFIC LAWS MUST BE FOLLOWED.

Key off.
Breakout box installed.
Reconnect PCM to breakout box.
Reconnect PSOM.
DVOM on 20 volt AC scale.
Warm engine to operating temperature.
Measure AC voltage between Test Pin 3 and Test Pin 6 while gradually increasing vehicle speed to 50 mph.

Is the maximum voltage received greater than 4.0 volts?

Yes	No
REPLACE PCM. REMOVE breakout box. RERUN Quick Test.	REMOVE breakout box. RECONNECT components. REFER to the Instrument Cluster, Speed Control or Brake Group in the Service Manual for further diagnosis.