Programmable Speedometer/Odometer Module (PSOM)

1997 PCED OBDII-Diesel

SECTION 5C: Pinpoint Tests

J: Programmable Speedometer/Odometer Module (PSOM)

J1 DIAGNOSTIC TROUBLE CODE (DTC) P0500: 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.
Set NGS Tester for frequency measurement with a 4 volt DC scale.
Attach NGS Tester probes across Test Pins 33 and 58.
Drive vehicle at 40 mph or 60 mph.

Does frequency read 90 Hz at 40 mph or 130 Hz at 60 mph (±2 Hz)?

Yes	No
REPLACE PCM. REMOVE breakout box. RERUN Scan Tool Diagnostic Test.	GO to J2.

J2 CHECK PSOM RESISTANCE

Possible error in the PSOM output signal.
Possible causes:

rear anti-lock brake system (RABS) sensor
PSOM
wiring harness
PCM

Key off.
Disconnect PCM. Inspect for damaged or pushed-out pins, corrosion and loose wires. Service as necessary.
Install breakout box. Leave PCM disconnected.
Measure resistance between Test Pin 58 and Test Pin 33 at the breakout box.

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

Yes	No
REPLACE PCM. REMOVE breakout box. RERUN Scan Tool Diagnostic Test.	GO to J3.

J3 CHECK CONTINUITY OF THE HARNESS CIRCUITS

Key off.
Breakout box installed, PCM disconnected.
Disconnect PSOM.
Measure resistance between Test Pin 58 at the breakout box and Pin 7, PSOM (+), circuit 697 (GY/BK) at the PSOM vehicle harness connector.
Measure resistance between Test Pin 33 at the breakout box and Pin 2, PSOM (-), circuit 676 (PK/O) at the PSOM vehicle harness connector.

Is each resistance less than 5 ohms?

Yes	No
GO to J4.	SERVICE open circuit. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test.

J4 CHECK HARNESS CIRCUITS FOR SHORTS TO POWER AND GROUND

Key off.
Breakout box installed, PCM disconnected.
PSOM disconnected.
Measure resistance between Test Pin 58 and Test Pins 33, 71 and 51 at the breakout box.

Is each resistance greater than 10,000 ohms?

Yes	No
REMOVE breakout box. RECONNECT components. REFER to the Electrical/Instrumentation and Warning System Group, the Powertrain/Fuel System Group, or the Chassis/Brake System Group in the Service Manual.	SERVICE short circuit. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test.