Test Procedure
WARNING: This page does not describe the selected car, but rather 30 other vehicles, including the 2004 Mercury Sable, 2004 Mercury Mountaineer, 2004 Mercury Monterey, 2004 Mercury Marauder, and 2004 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.
- JH1 CHECK THE CTO SIGNAL FROM THE PCM
- Disconnect the instrument cluster harness connector.
- PCM connector connected.
- Key ON Engine RUN.
- Measure voltage between the CTO pin 48 at the instrument cluster and battery negative post.
Is the voltage between 3 and 9 volts?
Yes No REFER to the appropriate INSTRUMENT CLUSTER article for diagnosis and testing. KEY OFF.
GO to JH2. - JH2 CHECK THE CTO FOR A SHORT TO POWER IN THE HARNESS
- PCM connector disconnected.
- Measure the resistance between:
( + )PCM Connector, Harness Side ( - )PCM Connector, Harness Side CTO - Pin 48 VPWR - Pin 71 CTO - Pin 48 VREF - Pin 90 Are the resistances greater than 10K ohms?
Yes No KEY OFF.
GO to JH3.KEY OFF. REPAIR short circuit to PWR. - JH3 CHECK THE CTO CIRCUIT FOR A SHORT TO GROUND
- Measure the resistance between:
( + )PCM Connector, Harness Side ( - )PCM Connector, Harness Side CTO - Pin 48 PWRGND - Pin 103 CTO - Pin 48 SIGRTN - Pin 91 Are the resistances greater than 10K ohms?
Yes No GO to JH4. REPAIR short circuit to GND. - JH4 CHECK THE CTO CIRCUIT FOR AN OPEN IN THE HARNESS
- CHECK the CTO circuit resistance.
Is the resistance less than 5 ohms?
Yes No GO to JH5. REPAIR open circuit. - JH5 CHECK THE CTO CIRCUIT FOR INTERMITTENT FAULTS
- Lightly tap on the CTO and wiggle the harness connector to simulate road shock.
- Measure the CTO resistance between the PCM and the instrument cluster.
Is the resistance less than 5 ohms?
Yes No KEY OFF. INSTALL a new PCM.
Refer to FLASH ELECTRICALLY ERASEABLE PROGRAMMABLE READ ONLY MEMORY - FLASH EEPROM .KEY OFF. REPAIR open circuit.