P1235 - Fuel Pump Control Out Of Range
Note: For LS6/LS8 and Thunderbird, the FPDM functions are incorporated in the Rear Electronics Module (REM). Also, the REM does not use a FPM circuit. Diagnostic information will be sent through SCP.
P1235 indicates that the FPDM has detected an invalid or missing FP circuit signal from the PCM. The FPDM will send a message to the PCM through the FPM circuit, indicating that this failure has been detected. The PCM will set the DTC when the message is received.
- FP circuit open or shorted
- Electronic Throttle Control (ETC) system concern (check for ETC DTC P2105).
- Damaged FPDM.
- Damaged PCM
- The FPDM sends a 25% duty cycle (250 msec ON, 750 msec OFF) through the FPM circuit to the PCM while the fault is being detected by the FPDM. If the fault is no longer detected, the PDM will return to sending an "all OK" (50% duty cycle) message to the PCM. The PCM will keep P1235 stored in Continuous Memory.
- For LS6/LS8 and Thunderbird, check if Electronic Throttle Control (ETC) DTC P2105 is present. An ETC system concern could cause a P1235, and should be diagnosed first.
KB1 DTC P1233 OR P1234: IS DTC P1233 OR P1234 PRESENT IN KEY ON ENGINE OFF SELF TEST
Is DTC P1233 or P1234 present in Key On Engine Off Self-Test?
Yes
No
A hard fault is present. GO to KB2 .
The PCM is now receiving a signal from the FPDM. One possible cause of the DTC P1233 or P1234 is that the IFS switch was tripped, then reset.
If engine is now a no start:
Disregard the DTC P1233 or P1234 at this time. RETURN to Section 3 and CONTINUE as directed. After servicing the no start, to diagnose intermittent causes of the DTC P1233 or P1234, RETURN to GO to KB25 .
If engine will start:
GO to KB25 to diagnose intermittent condition.
KB2 DOES THE ENGINE START?
Does the engine start?
Yes
No
GO to KB15 (to check the FPM circuit).
VERIFY IFS switch is set (button depressed). If OK, GO to KB3 .
KB3 CHECK POWER AND GROUND CIRCUITS TO FPDM
- Disconnect FPDM.
- Key on, engine off.
- Measure voltage between the FPDM PWR pin and ground pin at the FPDM harness connector.
Is voltage greater than 10.5 volts?
Yes
No
Key off. REPLACE FPDM.
GO to KB4 .
KB4 CHECK POWER TO FPDM
- Key on, engine off.
- Measure voltage between the FPDM PWR pin at the FPDM harness connector and chassis ground.
Is voltage greater than 10.5 volts?
Yes
No
REPAIR open ground circuit to FPDM.
KEY OFF. No power to FPDM.
For Escort, Mustang:
GO to KB5 .
All Others:
GO to KB8 .
KB5 CHECK B+ VOLTAGE TO CCRM PIN 11 (FPDM POWER SUPPLY RELAY)
- Disconnect CCRM.
- Measure B+ circuit voltage at Pin 11 of the CCRM harness connector.
Is voltage greater than 10.5 volts?
Yes
No
For Mustang:
GO to KB6 .
For Escort:
GO to KB7 .
VERIFY integrity of related fuse. If OK, REPAIR open B+ circuit. If fuse is damaged, CHECK B+ and FPDM PWR circuits for short to ground before replacing.
KB6 CHECK GROUND CIRCUIT TO CCRM PIN 18
- Measure resistance of ground circuit between CCRM harness connector Pin 18 and chassis ground.
Is resistance less than 5.0 ohms?
Yes
No
GO to KB7 .
SERVICE open ground circuit.
KB7 CHECK FOR OPEN FPDM PWR CIRCUIT
- Measure resistance of FPDM PWR circuit between CCRM harness connector (pin 5) and FPDM harness connector.
Is resistance less than 5.0 ohms?
Yes
No
REPLACE CCRM.
The FPDM PWR circuit is open. GO to KB13 to help isolate fault.
KB8 CHECK B+ VOLTAGE TO FPDM POWER SUPPLY RELAY
- Disconnect FPDM power supply relay.
- Measure B+ circuit voltage at the FPDM power supply relay harness connector.
Is voltage greater than 10.5 volts?
Yes
No
GO to KB9 .
VERIFY integrity of related fuse. If OK, REPAIR open B+ circuit. If fuse is damaged, CHECK B+ and FPDM PWR circuits for short to ground before replacing.
KB9 CHECK FOR GROUND TO FPDM POWER SUPPLY RELAY
- Disconnect scan tool from DLC.
- Measure resistance of ground circuit between FPDM power supply relay harness connector and battery negative post.
Is resistance less than 5.0 ohms?
Yes
No
GO to KB10 .
REPAIR open circuit.
KB10 CHECK FOR OPEN FPDM PWR CIRCUIT
- Measure resistance of FPDM PWR circuit between FPDM power supply relay harness connector and FPDM harness connector.
Is resistance less than 5.0 ohms?
Yes
No
RECONNECT FPDM. GO to KB11 .
The FPDM PWR circuit is open. GO to KB13 to help isolate fault.
KB11 CHECK VPWR CIRCUIT VOLTAGE (IGN START/RUN for Taurus/Sable) TO FPDM POWER SUPPLY RELAY
- Key on, engine off.
- Measure VPWR circuit voltage (IGN START/RUN for Taurus/Sable) at the FPDM power supply relay harness connector.
Is voltage greater than 10.5 volts?
Yes
No
REPLACE FPDM power supply relay.
REPAIR open VPWR (or IGN START/RUN) circuit.
KB13 ISOLATE OPEN IN FPDM PWR CIRCUIT
- Disconnect IFS switch.
- Measure resistance of FPDM PWR circuit between IFS switch harness connector and FPDM power supply relay harness connector (for Escort and Mustang, CCRM harness connector [pin 5]).
- Measure resistance of FPDM PWR circuit between FPDM harness connector and IFS switch harness connector.
Are both resistances less than 5.0 ohms?
Yes
No
VERIFY that the IFS switch is set (button depressed). If OK, REPLACE IFS switch.
REPAIR open in appropriate area of FPDM PWR circuit.
KB15 CHECK FOR OPEN FPM CIRCUIT
Note: Refer to the PCM connector pin numbers in the beginning of this pinpoint test.
- Disconnect FPDM.
- Disconnect PCM.
- Measure resistance of FPM circuit between PCM harness connector and the FPDM harness connector.
Is resistance less than 5.0 ohms?
Yes
No
GO to KB16 .
REPAIR open circuit.
KB16 CHECK FPM CIRCUIT FOR SHORT TO POWER IN HARNESS
- Key on, engine off.
- Measure voltage between FPM circuit at the PCM harness connector and ground.
Is voltage less than 1.0 volt?
Yes
No
KEY OFF. GO to KB17 .
REPAIR short circuit.
KB17 CHECK FPM CIRCUIT FOR SHORT TO GROUND IN HARNESS
- Disconnect scan tool from DLC.
- Measure resistance between FPM circuit at the PCM harness connector and ground.
Is resistance greater than 10,000 ohms?
Yes
No
GO to KB18 .
REPAIR short circuit.
KB18 CHECK FOR FPM OUTPUT FROM FPDM
- Reconnect FPDM.
- Key on, engine off.
- Measure dc voltage between FPM circuit at the PCM harness connector and ground.
Is voltage between 0.02 and 1.0 volt dc? (It is OK for the voltage to cycle below this range and then return to within range.)
Yes
No
REPLACE PCM (refer to Section 2, Flash Electrically Erasable Programmable Read Only Memory (EEPROM) ).
REPLACE FPDM.
KB25 CHECK CIRCUITS THAT MAY CAUSE AN INTERMITTENT LOSS OF POWER SUPPLY TO THE FPDM. ALSO CHECK FOR INTERMITTENT OPENS OR SHORTS ON THE FPM CIRCUIT.
Note: Be aware that P1233/1234 could be set if the inertia fuel shutoff (IFS) switch was tripped then reset.
Your best bet , take it to a qualified repair shop.
C1123
Vehicle Speed Circuit Fault
Overhead Console Module
REFER to Section 413-08 .
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