Pinpoint Test B: DTC P1572 Or DTC P1703 - Brake On/Off Circuit Failure

WARNING: This page is about a different car, the 2006 Mercury Grand Marquis and 2006 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.

B1 CHECK THE OPERATION OF THE STOPLAMPS
- Key in ON position.
- Operate the stoplamps.
- Do the stoplamps operate correctly?
Yes : GO to B2.

No : REFER to EXTERIOR LIGHTING to continue diagnosis of the stoplamps.
B2 CHECK THE SPEED CONTROL DEACTIVATOR SWITCH FOR CORRECT OPERATION
- Key in OFF position.
- Disconnect: PCM C175b.
- While firmly applying and releasing the brake pedal, measure the voltage between the PCM C175b-7, circuit 636 (OG), harness side and ground.
  
  Fig 1: Measuring Voltage Between PCM C175B-7, Circuit 636 (OG), Harness Side And Ground
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts with the brake pedal released and 0 volts with the brake pedal firmly applied?
Yes : GO to B6.

No : GO to B3.
B3 CHECK CIRCUIT 22 (LB/BK) FOR AN OPEN
- Disconnect: Speed Control Deactivator Switch C277.
- Measure the voltage between the speed control deactivator switch C277-2, circuit 22 (LB/BK), harness side and ground.
  
  Fig 2: Measuring Voltage Between Speed Control Deactivator Switch C277-2, Circuit 22 (LB/BK) And Ground
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts?
Yes : GO to B4.

No : VERIFY the CJB fuse 5 (10A) is OK. If OK, REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
B4 CHECK CIRCUIT 636 (OG) FOR A SHORT TO VOLTAGE
- Key in ON position.
- Measure the voltage between the speed control deactivator switch C277-1, circuit 636 (OG), harness side and ground.
  
  Fig 3: Measuring Voltage Between Speed Control Deactivator Switch C277-1, Circuit 636 (OG) And Ground
  Courtesy of FORD MOTOR CO.
- Is any voltage present?
Yes : REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.

No : GO to B5.
B5 CHECK CIRCUIT 636 (OG) FOR AN OPEN
- Key in OFF position.
- Measure the resistance between the speed control deactivator switch C277-1, circuit 636 (OG), harness side and the PCM C175b-7, circuit 636 (OG), harness side.
  
  Fig 4: Measuring Resistance Between Speed Control Deactivator Switch C277-1, Circuit 636 (OG) And PCM C175B-7, Circuit 636 (OG)
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
Yes : INSTALL a new speed control deactivator switch. REFER to SPEED CONTROL DEACTIVATOR SWITCH . CLEAR the DTCs. REPEAT the self-test.

No : REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
B6 CHECK FOR CORRECT PCM OPERATION
- Disconnect all the PCM connectors.
- Check for:
  - corrosion
  - pushed-out pins
- Connect all the PCM connectors and make sure they are seated correctly.
- Operate the system and verify the concern is still present.
- Is the concern still present?
Yes : INSTALL a new PCM. REFER to ELECTRONIC ENGINE CONTROLS .

No : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.