Unable to Activate Self Test/SCP Communication Error/DTC Not Listed

1997 PCED OBDII-Diesel

SECTION 5C: Pinpoint Tests

AF: Unable to Activate Self Test/SCP Communication Error/DTC Not Listed

AF: Introduction

AF1 DIAGNOSTIC TROUBLE CODE (DTC) P1502 — VERIFY SELF TEST ACTIVATION METHOD USED

Verify that the correct procedure was used to activate KOEO or KOER Self Test for the NGS Tester.

Note: Verify NGS Tester operation on another vehicle before proceeding.

Was the correct procedure used?

Yes	No
Correct procedure for activating self test was used. GO to AF2.	REFER to Scan Tool Diagnostic Test Procedures section for correct operating procedures.

AF2 CHECK PCM OUTPUT

Note: NGS Tester will kick out if battery voltage drops below 9.5 volts. If performing repeated self testing, unplug glow plug relay to prevent the battery from going dead, and disregard glow plug codes while glow plug relay is unplugged. If equipped with auxiliary powertrain control system, it must be off or disconnected while trying to perform self test.

Verify that batteries are fully charged and are not the cause of the communication error.

Does engine start?

Yes	No
GO to AF3.	GO to B1.

AF3 CHECK B+ AT DATA LINK CONNECTOR (DLC)

Key off.
Inspect the DLC for damage. Service as necessary.
Measure resistance between B+ circuit cavity at DLC Pin 16 and battery positive post.
Key off.

Is resistance less than 5 ohms?

Yes	No
GO to AF4.	SERVICE open in DLC B+ circuit. RERUN Quick Test.

AF4 CHECK DLC CHASSIS GROUND CONTINUITY

Key off.
Measure resistance between chassis ground circuit cavity at DLC Pin 4 and ground.

Is resistance less than 5.0 ohms?

Yes	No
GO to AF5.	SERVICE open in DLC chassis ground circuit. RERUN Quick Test.

AF5 CHECK DLC PWR GND CIRCUIT CONTINUITY

Key off.
Disconnect PCM. Inspect for damaged or pushed-out pins, loose wires and corrosion. Service as necessary.
Install breakout box. Leave PCM disconnected.
Measure resistance between Test Pin 51, 76, 77, 103 (PWR GND) at the breakout box and the PWR GND circuit cavity at the DLC Pin 5.

Is resistance less than 5.0 ohms?

Yes	No
GO to AF6.	SERVICE open in DLC PWR GND circuit. RECONNECT the PCM. REMOVE breakout box. RERUN Quick Test.

AF6 CHECK DLC BUS(-) CIRCUIT CONTINUITY

Key off.
Breakout box installed, PCM disconnected.
Measure resistance between Test Pin 15 [BUS(-)] at the breakout box and the BUS(-) circuit at the DLC Pin 10.

Is resistance less than 5.0 ohms?

Yes	No
GO to AF7.	SERVICE open in the DLC BUS (-) circuit. RECONNECT the PCM. REMOVE breakout box. RERUN Quick Test.

AF7 CHECK BUS(-) CIRCUIT FOR SHORT TO GROUND

Key off.
Breakout box installed, PCM disconnected.
Measure resistance between Test Pin 15 [BUS(-)] at the breakout box and ground.

Is resistance greater than 10,000 ohms?

Yes	No
GO to AF8.	SERVICE short to ground in the BUS(-) circuit. RECONNECT the PCM. REMOVE breakout box. RERUN Quick Test.

AF8 CHECK BUS(-) CIRCUIT FOR SHORT TO POWER

Key off.
Breakout box installed, PCM disconnected.
Key on, engine off.
Measure voltage between Test Pin 15 [BUS(-)] and Test Pin 51/76/77 or 103 (PWR GND) at the breakout box.

Was the voltage greater than 1.0 volt?

Yes	No
SERVICE short to power in the BUS(-) circuit. RECONNECT the PCM. REMOVE breakout box. RERUN Quick Test.	GO to AF9.

AF9 CHECK DLC BUS(+) CIRCUIT CONTINUITY

Key off.
Breakout box installed, PCM disconnected.
Measure resistance between Test Pin 16 [BUS(+)] at the breakout box and BUS(+) circuit at the DLC Pin 2.

Is resistance less than 5.0 ohms?

Yes	No
GO to AF10.	SERVICE open in DLC BUS(+) circuit. RECONNECT the PCM. REMOVE breakout box. RERUN Quick Test.

AF10 CHECK BUS(+) CIRCUIT FOR SHORT TO POWER

Key off.
Breakout box installed, PCM disconnected.
Key on, engine off.
Measure voltage between Test Pin 16 [BUS(+)] and Test Pins 51, 76, 77 or 103 (PWR GND) at the breakout box.

Was the voltage greater than 1.0 volt?

Yes	No
SERVICE short to power in the BUS(+) circuit. RECONNECT the PCM. REMOVE breakout box. RERUN Quick Test.	GO to AF11.

AF11 CHECK BUS (+) AND BUS (-) SHORTED TOGETHER

Key off.
Breakout box installed, PCM disconnected.
Measure resistance between Pins 15 and 16 at the breakout box.

Is resistance greater than 10,000 ohms?

Yes	No
CLEAR DTCs and RETEST. If DTC P1502 is still present, or if still unable to perform Self Test, REPLACE PCM.	REPAIR short between BUS + and BUS - circuits.