Front Control Module (FCM)

B2122-IGNITION RUN CONTROL 1 CIRCUIT LOW





For a complete wiring diagram, refer to the Wiring Information Electrical Diagrams.

Theory of Operation

The family of B2100 Diagnostic Trouble Codes (DTCs) typically describes ignition performance related faults. These are often caused by a contradiction of switch status information. For example, if an Electronic Control Unit (ECU) receives a bussed message indicating ignition switch position but the state of a hardwired ignition circuit indicates another switch position a B2100 series DTC would likely result.

These DTCs can be caused by a number of conditions including:

- loose connections
- missing or blown fuses
- faulty component
- vehicle no start or long crank time

Verify the proper operation of the starting system and verify that this DTC is active before proceeding with the diagnostic test.

- When Monitored:
With the ignition on.

- Set Condition:
The Front Control Module (FCM) will set this if the Left Trailer Tow Brake Lamp Relay Control circuit is shorted to ground for greater than 2 seconds.





1. CHECK FOR ACTIVE DTC
1. With the scan tool, read the active DTCs.
2. Cycle the ignition switch from off to on, leaving the ignition on for a minimum of 90 seconds.
3. With the scan tool, read the active DTCs.

Does the scan tool display this DTC as active?

Yes

- Go To 2

No

- If the DTC is stored, check for an intermittent condition. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

2. LEFT TRAILER TOW RELAY
1. Turn the ignition off.
2. Install a substitute relay in place of the original Left Trailer Tow Relay.
3. Cycle the ignition switch from off to on, leaving the ignition on for a minimum of 90 seconds.
4. With the scan tool, read the active FCM DTCs.

Does the scan tool display this DTC as active?

Yes

- Replace the FCM.
- Perform the BODY VERIFICATION TEST. Body Verification Test.

No

- Replace the original Left Trailer Tow Relay.
- Perform the BODY VERIFICATION TEST. Body Verification Test.