03 cobra will not stop thowing P1235 DTC

[Dawgstang]

Recently finished installing a TVS SC and all the supporting mods. Fuel mods include 60il injectors,Fore fuel hat with GT pumps and LP dual FPDM wiring harness. Anyways, have gone through 4 revised mail order tunes and car will not stop throwing the P1235 DTC. I did some research on this code and understand that the FPDM is not receiving a valid control duty cycle signal from the PCM. The tuner does not no why my car continues to throw the code. Is there anything I can replace or check to try and resolve this issue.

 

[03 TOPLESSSVT]

Something is not wired correctly at the Dual FPDM harnessing.

 

[testorossa1989]

op:

 

[01Jes]

Nvrmind

 

[Dawgstang]

Nearly impossible to screw up Lethal's dual FPDM wiring harness installation. It is basically plug and play. Funny thing is, the code will not come on if I let the car warm up at idle, then drive it around. The code is triggered if I start driving the car while the engine is cold. I know, problem solved. Don't hit the gas until engine is warmed up.

 

[Dawgstang]

My other problem is when the car is at WOT my A/F ratio stays right at 10 and does not move. My tuner is working on that problem though. Maybe those two problems are related.

 

[hotcobra03]

some info from ford manual...



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.

KB30 DTC P1235 OR P1236: IS DTC P1235 OR P1236 PRESENT IN KEY ON ENGINE OFF OR ENGINE RUNNING SELF TEST?
Note: Refer to the PCM connector pin numbers in the beginning of this pinpoint test.

Note: For LS6/LS8 and Thunderbird, check if Electronic Throttle Control (ETC) DTC P2105 is present. An ETC system concern could cause a P1235/P1236, and should be diagnosed first.

Is DTC P1235 or P1236 present in Key On Engine Off or Engine Running Self-Test?
Yes No
A hard fault is present. GO to KB31 to check the FP circuit. DTC P1235 or P1236 is intermittent.

For LS6/LS8 and Thunderbird :

GO to KB42 .

All others :

GO to KB45 .

KB31 CHECK FOR OPEN FP CIRCUIT BETWEEN PCM AND FPDM
Note: For LS6/LS8 and Thunderbird, the FPDM functions are incorporated in the Rear Electronics Module (REM). In the following steps, if directed to perform an action with the FPDM, complete the action with the REM. Refer to the pin numbers in the beginning of this pinpoint test.

Disconnect FPDM.
Disconnect PCM.
Measure resistance of FP circuit between PCM harness connector pin and the FPDM harness connector.
Is resistance less than 5.0 ohms?
Yes No
GO to KB32 . REPAIR open circuit.

KB32 CHECK FP CIRCUIT FOR SHORT TO POWER IN HARNESS
Key on, engine off.
Measure voltage between FP circuit at PCM harness connector pin and ground.
Is voltage less than 1.0 volt?
Yes No
KEY OFF. GO to KB33 . REPAIR short circuit.

KB33 CHECK FP CIRCUIT FOR SHORT TO GROUND IN HARNESS
Disconnect scan tool from DLC.
Measure resistance between FP circuit at PCM harness connector pin and ground.
Is resistance greater than 10,000 ohms?
Yes No
For LS6/LS8 and Thunderbird :

GO to KB36 .

All others :

GO to KB34 . REPAIR short circuit.

KB34 CHECK FP CIRCUIT IN FPDM
Reconnect FPDM.
Key on, engine off.
Measure voltage between FP circuit at PCM harness connector pin and ground.
Is voltage between 4.5 and 5.5 volts?
Yes No
REPLACE PCM (refer to Section 2, Flash Electrically Erasable Programmable Read Only Memory (EEPROM) ). REPLACE FPDM.

KB45 CHECK FP CIRCUIT FOR INTERMITTENT OPENS OR SHORTS
Key on, engine off.
Access FPM PID.
Note: With no fault detected, the FPDM will send a 50% duty cycle signal (all OK) to the PCM on the FPM circuit. Depending on scan tools, the FPM PID may display 50%, or a random value that is fluctuating between 85 and 115%.

Observe the FPM PID for an indication of a fault while completing the following (look for the FPM PID to change from the 50% value, or to stop fluctuating):
Shake, wiggle, bend the FP circuit between FPDM and the PCM.
Lightly tap on the FPDM (to simulate road shock).
Is a fault indicated?
Yes No
ISOLATE fault and REPAIR as necessary. KEY OFF. Unable to duplicate or identify fault at this time. GO to Z1 .

 

[Black306]

Bypass the harness by plugging the factory FPDM connector into one of the FPDMs. It'll only run one pump and some of the fuel will backflow through the non-running pump, but the car should start. I wouldn't suggest driving it though; only do that to see if it gets rid of the code.

 

[Dawgstang]

I'm still hoping once my tune is dialed in correctly, the code disappears. My WOT is still too rich at 10, instead of 11.5 - 12.

 

[Black306]

A P1235 code has nothing to do with a tune. A P1235 code is basically the FPDM telling the ECU 'I don't understand what you're telling me.' The ECU is suppose to send out a pulse modulated signal either between 5-51% (for fuel pump duty cycle) or between 67.5-82.5% (stop the pumps). Anything between 0-5%, 51-67.5%, or 82.5-100% the ECU wont send. If it does, then the P1235 code comes up.

If I were to guess, you might have a loose connection for pin 1 in the harness. By eliminating the harness, you remove a variable that might be making that code pop up.

 

[Anabolic]

^ great advice.

 

[Dawgstang]

Good advice, I will look into those possible problems. I will closely look at all the connections and check for bent pins in the connectors.

 

[Dawgstang]

Finally fixed problem. Bottom line do not have both FPDMs (master&slave) communicating with ECU. If you do, code P1235 will be triggered.

 

[hotcobra03]

Finally fixed problem. Bottom line do not have both FPDMs (master&slave) communicating with ECU. If you do, code P1235 will be triggered.

the fix was change in tune,,or change in wiring?

 

[Dawgstang]

The fix was in the wiring.