Pinpoint Test D: DTC C1985 - Back Up Aid Disable Switch Stuck Low

WARNING: This page is about a different car, the 2010 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.

Refer to appropriate SYSTEM WIRING DIAGRAMS article, Parking Aid for schematic and connector information.

Normal Operation

The parking aid system is disabled when the operator selects PARK AID OFF through the message center. The parking aid system remains disabled until either the ignition key is cycled from OFF to RUN, or PARK AID ON is selected through the message center. A reference voltage is sent from the instrument cluster (IC) to the parking aid module (PAM) on circuit 1435 (DG/VT) indicating that a PARK AID OFF request has been made. The PAM generates a reference voltage to the IC on circuit 1436 (VT/OG) indicating that the request has been received, and the system has been disabled.

DTC C1985 (Back Up Aid Disable Switch Stuck Low) - is a continuous and on-demand DTC that sets if the PAM detects a short to ground on the disable request circuit 1435 (DG/VT).

This pinpoint test is intended to diagnose the following:

Wiring, terminals or connectors
Parking aid system inline harness
PAM

PINPOINT TEST D: DTC C1985 - BACK UP AID DISABLE SWITCH STUCK LOW

CAUTION: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.

NOTE: Diagnostic measurements are made at the parking aid system inline harness connector located in the luggage compartment, forward of the LH tail light assembly.

D1 CHECK THE RECORDED DTCs FROM BOTH THE CONTINUOUS AND ON-DEMAND PAM SELF-TESTS
- Check the recorded DTCs from the PAM self-test.
- Are any DTCs recorded?
1. YES : If DTC C1985, go to D2.
  All other DTCs, REFER to DTC Index .
2. NO : Go to Pinpoint Test A .
D2 RETRIEVE THE RECORDED DTCs FROM BOTH THE CONTINUOUS AND ON-DEMAND PAM SELF-TESTS
- Key in OFF position.
- Disconnect: ICC220
- Key in ON position.
- Retrieve the recorded PAM DTCs from the on-demand self-test.
- Are any DTCs recorded?
1. YES : If DTC C1985, go to D3.
  All other DTCs, REFER to DTC Index .
2. NO : INSTALL a new IC. REFER to INSTRUMENTATION, MESSAGE CENTER, & WARNING CHIMES article.
D3 CHECK CIRCUIT 1435 (DG/VT) FOR A SHORT TO GROUND
- Key in OFF position.
- Disconnect: Parking Aid System Inline Harness C406
- Measure the resistance between the parking aid system inline harness C406-2, circuit 1435 (DG/VT), body harness side and ground.
- Is the resistance less than 5 ohms?
1. YES : REPAIR the circuit. CLEAR the DTCs. REPEAT the self-test.
2. NO : Go to D4.
D4 CHECK THE PARKING AID SYSTEM INLINE HARNESS
- Inspect the parking aid system inline harness for an open, short to voltage, or short to ground.
- Is the parking aid system inline harness OK?
1. YES : Go to D5.
2. NO : INSTALL a new or REPAIR the parking aid system inline harness. CLEAR the DTCs. REPEAT the self-test.
D5 CHECK FOR CORRECT PAM OPERATION
- Disconnect the PAM connector.
- Check for:
  - corrosion
  - damaged pins
  - pushed-out pins
- Connect the PAM connector and make sure it seats correctly.
- Operate the system and determine if the concern is still present.
- Is the concern still present?
1. YES : INSTALL a new PAM. REFER to Parking Aid Module (PAM) . TEST the system for normal operation.
2. 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.