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Home >> GMC >> 2006 >> Sierra 1500 HD, RWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1339 (Trailer Brake Control System) >> Diagnostic Information and Procedures >> DTC C0870, C1112, C1113, C1114, or C1119 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2009 GMC Sierra, 2009 GMC Cab & Chassis Sierra, 2009 Chevrolet Silverado, and 2009 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
IMPORTANT: These diagnostics are based on having no trailer connected.
  1. Ignition OFF, disconnect the harness connector at the solid state relay.
  2. Test for less than 5 Ω of resistance between the ground circuit terminal B and ground.
    • If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition OFF, verify that a test lamp illuminates between the B+ circuit terminal F and ground.
    • If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the STUD 2 fuse is open, replace the trailer brake control relay.
  4. Ignition ON, verify that a test lamp does not illuminate between control circuit terminal E and ground.
    • If test lamp illuminates, test the control circuit for a short to voltage. If the circuit tests normal, replace the TBCM.
  5. Ignition ON, verify that a test lamp does not illuminate between control circuit terminal E and B+.
    • If test lamp illuminates, test the control circuit for a short to ground. If the circuit tests normal, replace the TBCM.
  6. Ignition ON, test for 3.2-4.1 V between the control circuit terminal C and ground.
    • If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the TBCM.
    • If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the TBCM.
  7. Ignition ON, test for 3.2-4.1 V between the control circuit terminal A and ground.
    • If less than the specified range, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the TBCM.
    • If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the TBCM.
  8. Ignition ON, test for less than 1 V between the control circuit terminal D and ground.
    • If greater than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the TBCM.
  9. If all circuits test normal, replace the trailer brake solid state relay.
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