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electrical ? 07 shelby C1446

mtflat

Flatheads Forever
2,559
147
This winter I've been having random warning light come on incidating low brake fluid level. Fluid isn't low.

Battery has trouble staying charged. Installed a new battery today and nothing has changed.

I always keep the alarm system on - don't know how much drain on the battery they cause.

Diagnostic pulls code C1446 - brake switch malfunction - open or short circuit. Doesn't appear to be any tsb's on this for mustangs that I could find.

Likely just the sensor on the side of the reservior and where do they disconnect from the harness? Or could it be related to the alarm system drawing current?

Any ideas? Thanks for anything you might have to offer.
 

blacksnapon

Moderator
Staff member
PINPOINT TEST E: DTC C1446 — BRAKE SWITCH CIRCUIT FAILURE
NOTICE: Use the Flex Probe Kit for all test connections to prevent damage to the wiring terminals. Do not use standard multi-meter probes.

Test Step Result / Action to Take
E1 MONITOR THE RED BRAKE WARNING INDICATOR
Ignition ON.
Observe the red brake warning indicator while turning the ignition switch from OFF to RUN.
Does the indicator illuminate for a brief period and then extinguish?
Yes
GO to E2.

No
REFER to Section 413-01 to diagnose the red brake warning indicator.
E2 CHECK THE ABS MODULE AND THE SJB FOR COMMUNICATION DTCs
Connect the scan tool.
Enter the following diagnostic mode on the scan tool: Self Test ABS Module.
Retrieve and record any ABS module communication DTCs.
Enter the following diagnostic mode on the scan tool: Self Test SJB.
Retrieve and record any SJB communication DTCs.
Are any communication DTCs present in the ABS module and/or the SJB?
Yes
For ABS module communication DTCs, REFER to the Anti-Lock Brake System (ABS) Module Diagnostic Trouble Code (DTC) Chart.

For SJB communication DTCs, REFER to the Master DTC Chart in Section 419-10.

No
GO to E3.
E3 CHECK FOR BPP SWITCH VOLTAGE TO THE ABS MODULE
Ignition OFF.
Disconnect: ABS Module C135.
Ignition ON.
While pressing and releasing the brake pedal, measure the voltage between ABS module C135-6, circuit 535 (LB/RD), harness side and ground.


Is the voltage greater than 10 volts with the pedal released and 0 volt with the pedal pressed?
Yes
GO to E12.

No
GO to E4.
E4 ISOLATE THE BPP SWITCH
Ignition OFF.
Disconnect: BPP Switch C278 (also known as the speed control deactivator switch).
While pressing and releasing the brake pedal, measure the resistance between BPP switch connector C278 pin-1, component side, and BPP switch C278 pin-2, component side.
Is the resistance greater than 10,000 ohms with the pedal pressed and less than 5 ohms with the brake pedal released?
Yes
GO to E5.

No
INSTALL a new BPP switch. REFER to Speed Control Deactivator Switch Removal and Installation in Section 310-03. CLEAR the DTC. REPEAT the self-test.
E5 CHECK CIRCUIT 535 (LB/RD) FOR AN OPEN
Ignition OFF.
Disconnect: PCM C175b.
Measure the resistance between ABS module C135-6, circuit 535 (LB/RD), harness side and BPP switch C278-1, circuit 535 (LB/RD), harness side.


Is the resistance less than 5 ohms?
Yes
GO to E6.

No
REPAIR circuit 535 (LB/RD). CLEAR the DTC. REPEAT the self-test.
E6 CHECK CIRCUIT 535 (LB/RD) FOR A SHORT TO GROUND
Measure the resistance between ABS module C135-6, circuit 535 (LB/RD), harness side and ground.


Is the resistance greater than 10,000 ohms?
Yes
GO to E7.

No
REPAIR circuit 535 (LB/RD). CLEAR the DTC. REPEAT the self-test.
E7 CHECK CIRCUIT 535 (LB/RD) FOR A SHORT TO VOLTAGE
Ignition ON.
Measure the voltage between ABS module C135-6, circuit 535 (LB/RD), harness side and ground.


Is any voltage present?
Yes
REPAIR circuit 535 (LB/RD). CLEAR the DTC. REPEAT the self-test.

No
GO to E8.
E8 CHECK THE PCM FOR A SHORT TO GROUND
Ignition OFF.
Connect: PCM C175b.
Measure the resistance between ABS module C135-6, circuit 535 (LB/RD), harness side and ground.


Is the resistance greater than 10,000 ohms?
Yes
GO to E9.

No
INSTALL a new PCM. REFER to Section 303-14. CLEAR the DTC. REPEAT the self-test.
E9 CHECK THE PCM FOR A SHORT TO VOLTAGE
Ignition ON.
Measure the voltage between ABS module C135-6, circuit 535 (LB/RD), harness side and ground.


Is any voltage present?
Yes
INSTALL a new PCM. REFER to Section 303-14. CLEAR the DTC. REPEAT the self-test.

No
GO to E10.
E10 CHECK CIRCUIT 391 (RD/YE) FOR AN OPEN
Ignition OFF.
Disconnect: BEC C1035a.
Measure the resistance between BPP switch C278-2, circuit 391 (RD/YE), harness side and BEC C1035a-C2, circuit 391 (RD/YE), harness side.


Is the resistance less than 5 ohms?
Yes
GO to E11.

No
VERIFY BEC fuse 47 (15A) is OK. If OK, REPAIR circuit 391 (RD/YE). CLEAR the DTC. REPEAT the self-test.
E11 CHECK CIRCUIT 391 (RD/YE) FOR A SHORT TO GROUND
Measure the resistance between BPP switch C278-2, circuit 391 (RD/YE), harness side and ground.


Is the resistance greater than 10,000 ohms?
Yes
INSTALL a new BPP switch. REFER to speed control deactivator switch in Section 310-03. CLEAR the DTCs. REPEAT the self-test.

No
REPAIR circuit 391 (RD/YE). CLEAR the DTC. REPEAT the self-test.
E12 CHECK FOR CORRECT ABS MODULE OPERATION
Ignition OFF.
Disconnect: ABS Module C135.
Check the ABS module connector for:
corrosion.
pushed-out pins.
spread terminals.
Connect: ABS Module C135.
Make sure the ABS module connector seats correctly, then operate the system and verify if the concern is still present.
Is the concern still present?
Yes
INSTALL a new ABS module. REFER to Anti-Lock Brake System (ABS) Module in this section. CLEAR the DTCs. REPEAT the self-test.

No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test with the brake pedal not applied.
 

mtflat

Flatheads Forever
2,559
147
Oh my - printed it out and will start sorting thru it. This was a lot easier when I could just look at the brake shoes and visually inspect them (grin)

Thank you sir, I appreciate it very much and I owe you.
 

blacksnapon

Moderator
Staff member
Oh my - printed it out and will start sorting thru it. This was a lot easier when I could just look at the brake shoes and visually inspect them (grin)

Thank you sir, I appreciate it very much and I owe you.
Theres another one on batteries discharging after storing the car for extended periods. It amounts to you needing to get an aftermarket battery tender (trickle charger)
 

mtflat

Flatheads Forever
2,559
147
That makes sense. I replaced the battery because it seemed to be losing its charge. First time it happened, was after sitting a couple of months and surviving -25F for a couple of days in an unheated garage. After that it would charge normally, but over a couple of weeks would be down again.

NAPA and CarQuest both said it tested good, but CQ did a top-off charge and after waiting 10 minutes it said it was down 14%. Another 10 minutes and without recharging, it said it was 100% again.

Just strange enough that I bought a new batt and will use the old one in a project truck IF it holds a charge.

Driving the car again today the brake switch malfunction lights are back on and then off randomly. It acts like there might be a broken connection.

I'll keep a trickle charger on it and see how it goes. Thanks!
 

mtflat

Flatheads Forever
2,559
147
Update for you Vince. I haven't taken time to run down diagnostics but I've been driving the car almost every day and the malfunction light has quit coming on - maybe the electrical system has just settled down from regular use.

I will keep a hard copy of your notes for future reference. Again, thanks for your time and trouble.

Also talked to the local Ford service manager and he suggested that if the mc reservoir isn't kept slightly over-full it can cause intermittent warnings as the fluid contracts and expands during cold/warm weather cycles. fwiw
 

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