Accelerator Pedal (AP) Sensor

1997 PCED OBDII-Diesel

SECTION 5C: Pinpoint Tests

E: Accelerator Pedal (AP) Sensor

E: Introduction

E1 DIAGNOSTIC TROUBLE CODE (DTC) P0123

DTC P0123 indicates AP sensor circuit high input.
Possible causes are:

damaged accelerator pedal assembly
AP sensor may not be seated properly (tightened down)
damaged AP sensor
short to power in harness
damaged PCM

Key on, engine off.
NGS Tester installed.
Access AP PID (voltage).
Slowly depress accelerator pedal while observing voltage reading on NGS Tester.

Does reading go above 4.5v?

Yes	No
GO to E2.	CLEAR DTCs and RETEST.

E2 INDUCE OPPOSITE FAILURE

Disconnect AP sensor connector. Inspect for damaged, pushed-out or corroded pins. Service as necessary.

Does AP voltage reading on NGS Tester read 0v?

Yes	No
Circuit OK. REPLACE accelerator pedal assembly. CLEAR DTCs and RETEST.	GO to E3.

E3 CHECK AP SENSOR SIGNAL WIRE

AP sensor disconnected.
Key on, engine off.
Measure voltage between AP signal wire at harness connector and ground.

Is voltage above 4.5v?

Yes	No
GO to E4.	REPLACE PCM. Internal failure. CLEAR DTCs and RETEST.

E4 CHECK AP CIRCUIT FOR SHORTS TO POWER

Key off.
AP sensor disconnected.
Disconnect PCM. Inspect for damaged or pushed-out pins, corrosion and loose wires. Service as necessary.
Install breakout box. Leave PCM disconnected.
Key on, engine off.
Measure voltage between Test Pin 89 and ground at the breakout box.

Is voltage present?

Yes	No
REPAIR short to power in Circuit 355 (GY/W). CLEAR DTCs and RETEST.	REPLACE PCM. Internal failure. CLEAR DTCs and RETEST.

E5 DIAGNOSTIC TROUBLE CODE (DTC) P0122

DTC P0122 indicates the AP sensor circuit low input.
Possible causes:

AP sensor may not be seated properly (tightened down)
damaged AP sensor
open harness
grounded harness
damaged PCM

Key on, engine off.
NGS Tester installed.
Access AP PID (voltage).
Depress accelerator pedal while observing voltage reading on NGS Tester.

Does voltage drop below 0.37v?

Yes	No
GO to E6.	Unable to duplicate and/or identify concern at this time. CLEAR DTCs and RETEST.

E6 INDUCE OPPOSITE FAILURE

Disconnect AP sensor connector and jumper VREF pin to AP signal wire.

Does NGS Tester display stay on and read over 4.5v?

Yes	No
REPLACE accelerator pedal assembly. CLEAR DTCs and RETEST.	GO to E7.

E7 CHECK VREF CIRCUIT VOLTAGE

Key off.
AP sensor disconnected.
Key on, engine off.
Measure voltage between VREF circuit and ground.

Is voltage 5v ± 0.5?

Yes	No
GO to E8.	SERVICE open in VREF Circuit 351 (BR/W). CLEAR DTCs and RETEST.

E8 CHECK AP GROUND CIRCUIT

Key off.
AP sensor disconnected.
Measure resistance between AP ground circuit and ground.

Is resistance less than 5 ohms?

Yes	No
GO to E9.	SERVICE open in AP ground Circuit 837 (Y/BK). CLEAR DTCs and RETEST.

E9 CHECK AP CIRCUIT CONTINUITY

Key off.
AP sensor disconnected.
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 AP circuit at the vehicle harness connector and Test Pin 89 at the breakout box, to the middle terminal.

Is the resistance less than 5 ohms?

Yes	No
GO to E10.	SERVICE open in AP signal Circuit 355 (GY/W). REMOVE breakout box. CLEAR DTCs and RETEST.

E10 CHECK AP CIRCUIT FOR SHORTS TO GROUND

Key off.
AP sensor disconnected.
Breakout box installed, PCM disconnected.
Measure resistance between Test Pin 89 and Test Pins 51, 76, 77, 91 and 103 at the breakout box.

Is each resistance greater than 10,000 ohms?

Yes	No
GO to E11. CLEAR DTCs and RETEST.	SERVICE short to ground in AP sensor signal Circuit 355 (GY/W). CLEAR DTCs and RETEST. REMOVE breakout box.

E11 VREF CIRCUIT CONTINUITY CHECK

AP sensor disconnected.
Breakout box installed, PCM disconnected.
Measure resistance between VREF circuit at harness connector and Pin 90 at the breakout box.

Is resistance less than 5 ohms?

Yes	No
GO to E12.	REPAIR open in VREF Circuit 351 (BR/W). CLEAR DTCs and RETEST.

E12 SIGNAL RETURN CIRCUIT CONTINUITY CHECK

AP sensor disconnected.
Breakout box installed, PCM disconnected.
Measure resistance between AP ground circuit at harness connector and Pin 24 at the breakout box.

Is resistance less than 5 ohms?

Yes	No
REPLACE PCM. CLEAR DTCs and RETEST.	REPAIR open in AP ground Circuit 837 (Y/BK).