Reference Voltage

1996 PCED OBDI

SECTION 18: Diesel Diagnosis — 7.3L DI Engine

B: Reference Voltage

B: Introduction

B1 CHECK VEHICLE BATTERY POWER CIRCUIT

Key off.
Disconnect PCM. Inspect for damaged or pushed-out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box and connect PCM to breakout box.
Key on, engine off.
Measure voltage between Test Pins 55, 71 and 97 to Test Pins 25, 51, 76, 77 and 103 at the breakout box. Note voltage.
Measure voltage across battery terminals. Note voltage.

Are both voltages greater than 10.5 volts, and are both voltages within 1.0 volt of each other?

Yes	No
GO to B2.	Key off, RECONNECT sensor (if applicable). GO to A1.

B2 CHECK VREF VOLTAGE

Key on, engine off.
Breakout box installed, PCM connected.
Measure voltage between Test Pin 90 and Test Pin 91 at the breakout box.

Is voltage between 4 volts and 6 volts?

Yes	No
GO to B3.	Less than 4 volts, GO to B5. Greater than 6 volts, GO to B4.

B3 CHECK VREF AND SIG RTN CIRCUITS FOR CONTINUITY

Key off.
Sensor that sent you here disconnected.
Breakout box installed.
Disconnect PCM.
Measure resistance between Test Pin 90 at breakout box and VREF circuit at vehicle harness connector of the sensor that sent you here.
Measure resistance between Test Pin 91 at breakout box and SIG RTN circuit at vehicle harness connector of the sensor that sent you here.

Is each resistance less than 5.0 ohms?

Yes	No
Reference voltage OK. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test.	SERVICE open in VREF or SIG RTN circuits. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test.

B4 CHECK FOR EXCESS VOLTAGE ON VREF CIRCUIT

Key off.
Breakout box installed.
Disconnect PCM.
Disconnect NGS Tester.
Key on, engine off.
Measure voltage between Test Pin 90 at the breakout box and battery ground.

Is voltage less than 0.5 volts?

Yes	No
REPLACE PCM. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test.	SERVICE short to power in vehicle harness. REMOVE breakout box. RECONNECT PCM and sensor. RERUN Scan Tool Diagnostic Test.

B5 SIG RTN CIRCUIT CHECK

Key off.
Breakout box installed.
PCM connected.
Measure resistance between Test Pin 91 and Test Pins 25, 51, 76, 77 and 103 at the breakout box.

Is each resistance less than 5 ohms?

Yes	No
GO to B6.	REPLACE PCM.

B6 CHECK FOR SHORTED ACCELERATOR PEDAL (AP) SENSOR

Key off.
Breakout box installed, PCM connected.
Disconnect AP sensor from vehicle harness.
Inspect for damaged or pushed-out pins.
Key on, engine off.
Measure voltage between Test Pin 90 and Test Pin 91 at the breakout box.

Is voltage less than 4.0 volts?

Yes	No
Leave AP sensor disconnected. GO to B7.	REPLACE AP sensor. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test.

B7 CHECK FOR SHORTED CAMSHAFT POSITION (CMP) SENSOR

Key off.
Breakout box installed, PCM connected.
Disconnect CMP sensor.
Inspect for damaged or pushed-out pins.
Key on, engine off.
Measure voltage between Test Pin 90 and Test Pin 91 at the breakout box.

Is voltage less than 4.0 volts?

Yes	No
Leave CMP sensor disconnected. GO to B8.	REPLACE CMP sensor. REMOVE breakout box. RECONNECT PCM and sensors. RERUN Scan Tool Diagnostic Test.

B8 CHECK FOR SHORTED INJECTION CONTROL PRESSURE (ICP) SENSOR

Key off.
Breakout box installed, PCM connected.
Disconnect ICP sensor.
Inspect for damaged or pushed-out pins.
Key on, engine off.
Measure voltage between Test Pin 90 and Test Pin 91 at the breakout box.

Is voltage less than 4.0 volts?

Yes	No
Leave ICP sensor disconnected. GO to B9.	REPLACE ICP sensor. REMOVE breakout box. RECONNECT PCM and sensor(s). RERUN Scan Tool Diagnostic Test.

B9 CHECK FOR SHORTED EXHAUST BACK PRESSURE (EBP) SENSOR

Key off.
Breakout box installed, PCM connected.
Disconnect EBP sensor.
Inspect for damaged or pushed-out pins.
Key on, engine off.
Measure voltage between Test Pin 90 and Test Pin 91 at the breakout box.

Is voltage less than 4.0 volts?

Yes	No
Leave EBP sensor disconnected. GO to B10.	REPLACE EBP sensor. REMOVE breakout box. RECONNECT PCM and sensor(s). RERUN Scan Tool Diagnostic Test.

B10 CHECK FOR SHORTED MANIFOLD ABSOLUTE PRESSURE MAP SENSOR

Key off.
Breakout box installed, PCM connected.
Disconnect MAP sensor.
Inspect for damaged or pushed-out pins.
Key on, engine off.
Measure voltage between Test Pin 90 and Test Pin 91 at the breakout box.

Is voltage less than 4.0 volts?

Yes	No
Leave MAP sensor disconnected. GO to B11.	REPLACE MAP sensor. REMOVE breakout box. RECONNECT PCM and sensor(s). RERUN Scan Tool Diagnostic Test.

B11 CHECK FOR SHORTED BAROMETRIC PRESSURE (BARO) SENSOR

Key off.
Breakout box installed, PCM connected.
Disconnect BARO sensor.
Inspect for damaged or pushed-out pins.
Key on, engine off.
Measure voltage between Test Pin 90 and Test Pin 91 at the breakout box.

Is voltage less than 4.0 volts?

Yes	No
Leave BARO sensor disconnected. GO to B12.	REPLACE BARO sensor. REMOVE breakout box. RECONNECT PCM and sensor(s). RERUN Scan Tool Diagnostic Test.

B12 CHECK VREF CIRCUIT FOR SHORT TO GROUND

Key off.
Breakout box installed.
Disconnect PCM.
With all six of the three-wire sensors (AP, CMP, ICP, EBP, MAP and BARO) disconnected, measure resistance between Test Pin 90 and Test Pins 25, 51, 76, 77, 91 and 103 at the breakout box.

Are all resistances greater than 10,000 ohms?

Yes	No
REPLACE PCM. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test.	SERVICE short to ground. REMOVE breakout box. RECONNECT all components. RERUN Scan Tool Diagnostic Test.