For 1990-2009 cars

# TCS Light Lit on IPC and DTC C1312 -- TCS Switch Bulb Open - ABS brake booster control EBTCM electrical light lens dim indicator off inoperative indicator part wire

Subject: | TCS Light Lit on IPC and DTC C1312--TCS Switch Bulb Open - ABS brake booster control EBTCM electrical lens dim indicator off inoperative indicator part wire

Models: | .

When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.

### Condition/Concern:

TCS indicator is lit on instrument panel cluster.

### Recommendation/Instructions:

The definition of DTC C1312 is TCS Enable Lamp Circuit Malfunction--checks the state of the TCS-off switch lamp circuit. If the TCS switch bulb is inoperative, replace bulb (PN 10287297) in the ORIGINAL switch.

Since there were no published diagnostics for C1312, refer to SI Document 678965. This may be helpful to understand how the TCS switch and bulb works. Replacing the switch assembly with a new one may result in switches without indicator bulbs or lamp-viewing window. There was a recent part change eliminating the lamp-viewing window.

Note: The amber TCS indicator in the instrument panel cluster does NOT illuminate when the TCS switch is turned off. This is an error in both the owners manual and the service manual. The only "ON" indicator is in the TCS switch lamp-viewing window. When the light is on in the switch, TCS is enabled. When switched off, the lamp is off in the switch and TCS is disabled.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance. This diagnostic approach was developed for the vehicle with the VIN you entered and should not be automatically be used for other vehicles with similar symptoms.