Ignition Control
B2105-IGNITION UNLOCK RUN/START CONTROL CIRCUIT HIGHB2105 - Ignition Unlock RUN/start Control Circuit High:
WHEN MONITORED
With the ignition on or off and with the FCM awake.
SET CONDITION
The Front Control Module will set this DTC within 2 seconds if the ignition unlock run/start circuit voltage is not what the expected value should be.
POSSIBLE CAUSES
- (F1) Fused ignition switch output (run start) circuit open
- (F1) Fused ignition switch output (run start) circuit shorted to voltage
- Powertrain control module (except 3.7L)
- Front control module
Theory of operation
The (F942) Fused Ignition Switch Output circuit supplies the FCM with battery power. The FCM processes the input and sends it out as the (F1) Fused Ignition Switch Output circuit to the Shift Lever assembly (3.7L) or the PCM (except 3.7L).
Diagnostic Test
1. CHECK FOR ACTIVE DTC
With the scan tool, read the active DTC's.
Cycle the ignition switch from off to on, leaving the ignition on for a minimum of 10 seconds then turn the ignition off.
With the scan tool, read the active DTC's.
Q: Does the scan tool display this DTC as active?
YES: Go To 2
NO: If the DTC is stored, check for an intermittent condition. Using the wiring diagram/schematic as a guide, visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals.
2. (F1) FUSED IGNITION SWITCH OUTPUT (RUN START) CIRCUIT SHORTED TO VOLTAGE
Disconnect the Powertrain Control Module C1 harness connector.
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.
Cycle the ignition switch from off to on then back to off.
NOTE: The ignition switch must be in the off position when performing the following step.
Using a 12-volt test light connected to ground, check the (F1) Fused Ignition Switch Output (Run Start) circuit.
Q: Does the test light illuminate brightly?
YES: Repair the (F1) Fused Ignition Switch Output (Run Start) circuit for a short to voltage. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 3
3. POWERTRAIN CONTROL MODULE
Turn the ignition on.
With the test light still connected from the previous step, check the (F1) Fused Ignition Switch Output (Run Start) circuit.
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool # 8815 to perform diagnosis.
Q: Does the test light illuminate brightly?
YES: Replace the Powertrain Control Module. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Go To 4
4. (F1) FUSED IGNITION SWITCH OUTPUT (RUN START) CIRCUIT OPEN
Turn the ignition off.
Remove the FCM from the Integrated Power Module.
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool # 8815 to perform diagnosis.
Measure the resistance of the (F1) Fused Ignition Switch Output (Run Start) circuit between the Powertrain Control Module C1 connector and the FCM-IPM connector.
Q: Is the resistance below 5.0 ohms?
YES: Inspect the wiring and connectors for damage or shorted circuits. If OK, replace and program the Front Control Module. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Repair the (F1) Fused Ignition Switch Output (Run Start) circuit for an open. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test