On Board Diagnostics II PCED

1999 PCED On Board Diagnostics II

SECTION 5: Pinpoint Tests

C: Reference Voltage

C: Introduction

C1 CHECK VREF CIRCUIT FOR SHORT TO PWR IN HARNESS

Disconnect TP sensor.
Key on.
Measure voltage between VREF and SIG RTN circuits at the TP sensor harness connector.

Is VREF greater than 6.0 volts?

Yes	No
KEY OFF. GO to C35 (to check VREF for short to power).	GO to C2 .

C2 CHECK VOLTAGE ON BATTERY

Measure voltage across battery terminals.

Is voltage greater than 10.5 volts?

Yes	No
GO to C3 .	Key off. REFER to Battery and Charging, Section 414-00 in the Workshop Manual to service discharged battery.

C3 CHECK VOLTAGE BETWEEN B+ AND SIG RTN

Disconnect sensor where VREF check failed.
Measure voltage between SIG RTN circuit and battery positive post at the appropriate sensor harness connector.

Is voltage greater than 10.5 volts and within 1.0 volt of battery voltage?

Yes	No
GO to C4 .	SIG RTN/PWR GND fault present. GO to C25 .

C4 CHECK VREF VOLTAGE THROUGH PCM ON TP PID

Note: For LS6/LS8 with multiple DTCs output, GO to C5 for VREF concerns.

Attempt to access the TP PID.

Can the PID be accessed?

Yes	No
KEY OFF. GO to C20 (to check VREF for opens).	GO to C5 (to check for VPWR, and VREF for shorts).

C5 CHECK VPWR VOLTAGE TO IAC VALVE

Disconnect TP sensor.
Disconnect idle air control (IAC) valve.
Key on.
Measure voltage between the VPWR circuit at the IAC valve harness connector and the battery negative post.

Is voltage greater than 10.5 volts?

Yes	No
RECONNECT IAC valve. For 2.0L Escort/Tracer, 2.0L Contour/Mystique, Cougar, 5.4L E/F-Series with NGV: GO to C7 . All Others: GO to C6 .	VPWR is not present. RECONNECT TP sensor. For application with Power Relay inside CCRM: GO to Pinpoint Test X1 . All others: GO to Pinpoint Test Step B1 .

C6 CHECK VREF CIRCUIT SHORT TO SIG RTN IN THE D.P.F. EGR OR EGR VALVE POSITION SENSOR

TP sensor disconnected.
Disconnect FTP sensor.
Key on.
Measure voltage between VREF and SIG RTN circuits at the TP sensor harness connector.

Is voltage between 4.0 and 6.0 volts?

Yes	No
KEY OFF. REPLACE D.P.F. EGR sensor or EGR valve position sensor.	For 3.0L FFV Taurus: GO to C12 . For all others: GO to C7 .

C7 CHECK VREF CIRCUIT SHORT TO SIG RTN IN FTP SENSOR

TP and D.P.F. EGR sensors disconnected.
Disconnect FTP sensor.
Key on.
Measure voltage between the VREF and SIG RTN circuits at the TP sensor harness connector.

Is voltage between 4.0 and 6.0 volts?

Yes	No
KEY OFF. REPLACE the FTP sensor.	For applications with an A/C Pressure (ACP) sensor: GO to C8 . For applications with PSP: GO to C9 . For applications with FRP only: GO to C10 . All Others: GO to C12 .

C8 CHECK VREF CIRCUIT SHORT TO SIG RTN IN ACP SENSOR

TP (FTP where applicable) and D.P.F. EGR sensor disconnected.
Disconnect ACP sensor.
Key on.
Measure voltage between the VREF and SIG RTN circuits at the TP sensor harness connector.
Key off.

Is voltage between 4.0 and 6.0 volts?

Yes	No
KEY OFF. REPLACE the ACP sensor.	For application with FRP: GO to C10 . All others: GO to C12 .

C9 CHECK VREF CIRCUIT SHORT TO SIG RTN IN PSP SENSOR

TP, FTP, ACP where applicable and D.P.F. EGR sensors disconnected.
Disconnect PSP sensor.
Key on.
Measure voltage between the VREF and SIG RTN circuits at the TP sensor harness connector.

Is voltage between 4.0 and 6.0 volts?

Yes	No
KEY OFF. REPLACE the PSP sensor.	For applications with FRP: GO to C10 . All others: GO to C12 .

C10 CHECK VREF CIRCUIT SHORT TO SIG RTN IN FRP SENSOR

TP, FTP, ACP and PSP where applicable and D.P.F. EGR sensors disconnected.
Disconnect fuel rail pressure (FRP) sensor.
Measure voltage between the VREF and SIG RTN circuits at the TP sensor harness connector.

Is voltage between 4.0 and 6.0 volts?

Yes	No
KEY OFF. REPLACE the FRP sensor.	KEY OFF. For applications with BARO: GO to C11 . All others: GO to C12 .

C11 CHECK VREF CIRCUIT SHORT TO SIG RTN IN BARO SENSOR

TP, D.P.F. EGR, FTP, and FRP disconnected.
Disconnect barometric (BARO) pressure sensor.
Measure voltage between VREF and SIG RTN circuits at the TP sensor harness connector.

Is voltage between 4.0 and 6.0 volts?

Yes	No
KEY OFF. REPLACE BARO sensor.	KEY OFF. GO to C12 .

C12 CHECK VPWR VOLTAGE TO PCM

Note: Refer to the PCM connector pin numbers in the beginning of this pinpoint test.

TP sensor disconnected.
All other sensors wired to VREF disconnected from previous test steps (if necessary, refer to Sensors Connected To VREF chart at the beginning of this pinpoint test).
PCM disconnected.
Key on.
Measure voltage between VPWR and PWR GND circuits at the PCM harness connector.

Is voltage greater than 10.5 volts?

Yes	No
GO to C13 .	KEY OFF. REPAIR open VPWR circuit between PCM and splice to IAC valve.

C13 CHECK VREF VOLTAGE FOR SHORT TO GROUND OR SIG RTN

TP sensor disconnected.
All other sensors wired to VREF disconnected.
Disconnect PCM.
Disconnect Scan Tool from DLC.
Measure resistance between VREF and SIG RTN, PWR GND circuits at the PCM harness connector. (For LS6/LS8 measure to both VREF pins.)

Is each resistance greater than 10,000 ohms?

Yes	No
REPLACE PCM (refer to Section 2 , Flash EEPROM).	REPAIR VREF short to ground.

C20 CHECK VREF CIRCUIT FOR OPEN IN HARNESS

Sensor where VREF check failed disconnected.
Disconnect PCM.
Measure resistance of VREF circuit between PCM harness connector pin and appropriate sensor harness connector.

Is resistance less than 5.0 ohms?

Yes	No
KEY OFF. REPLACE PCM (refer to Section 2 , Flash EEPROM).	REPAIR open VREF circuit. REFER to the EVTM and DTCs received to help pinpoint the location of the open.

C25 CHECK SIG RTN/PWR GND THROUGH PCM ON TP PID

Key on.
Attempt to access the TP PID.

Can the PID be accessed?

Yes	No
GO to C26 .	GO to C28 .

C26 ARE KOEO DTCs PRESENT FOR TWO OR MORE SENSORS/SWITCHES CONNECTED TO THE SIG RTN CIRCUIT?

Are KOEO DTCs present for two or more sensors/switches connected to the SIG RTN circuit? (Refer to the Electrical and Vacuum Troubleshooting Manual, Engine Controls.)

Yes	No
KEY OFF. GO to C27 .	KEY OFF. REPAIR open SIG RTN circuit to the sensor where the VREF check failed.

C27 CHECK SIG RTN CIRCUIT FOR OPEN IN HARNESS

Scan Tool disconnected.
Sensor where VREF check failed disconnected.
Disconnect PCM.
Measure resistance of SIG RTN circuit between PCM harness connector pin and appropriate sensor harness connector.

Is resistance less than 5.0 ohms?

Yes	No
RECONNECT sensor. GO to C28 .	REPAIR open SIG RTN circuit. REFER to the EVTM and DTCs received to help pinpoint the location of the open.

C28 CHECK PWR GND CIRCUITS FOR OPEN IN HARNESS

Disconnect scan tool from DLC.
Measure resistance of PWR GND circuits between the PCM harness connector pin and the battery negative post.

Is each resistance less than 5.0 ohms?

Yes	No
GO to C29 .	REPAIR open circuit.

C29 CHECK GROUND CIRCUITS FOR OPEN IN HARNESS

Measure resistance of ground circuits between SIG RTN and PWR GND circuits at the PCM harness connector.

Is each resistance less than 5.0 ohms?

Yes	No
SIG RTN/PWR GND circuits are OK in the harness and PCM. VERIFY results of previous test steps.	REPLACE PCM (refer to Section 2 , Flash EEPROM).

C35 CHECK VREF CIRCUIT FOR SHORT TO PWR

Sensor where VREF check failed disconnected.
Disconnect all other sensors connected to VREF (refer to Sensors Connected to VREF chart at beginning of this pinpoint test).
Disconnect PCM.
Key on.
Measure voltage between the VREF circuit at the TP sensor harness connector and the battery negative post.

Is voltage less than 0.5 volts?

Yes	No
KEY OFF. REPLACE PCM (refer to Section 2 , Flash EEPROM).	KEY OFF. REPAIR VREF short to power in harness.