Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Circuit/System Verification
- Ignition ON/Vehicle In Service Mode.
- Verify that DTC U0073, U0074, U0075, U0077, U0078, U007A, U007B, U007C, U007D, U1814, U2099, U2100, B1325, B1330, B1370, B1380, B1424, B1440, B1441, B1517, C0800, C0899, C12E1, P0560, P0562, P06E4, or P1EB9 is not set.
- If any of the DTCs are set
Refer to Diagnostic Trouble Code (DTC) List - Vehicle .
- Go to next step: If none of the DTCs are set
- If any of the DTCs are set
- Verify that the K56 Serial Data Gateway Module is communicating.
- If the K56 Serial Data Gateway Module is not communicating
Refer to Circuit/System Testing to diagnose the K56 Serial Data Gateway Module first.
- Go to next step: If the K56 Serial Data Gateway Module is communicating
- If the K56 Serial Data Gateway Module is not communicating
- Determine the device that is not communicating. Refer to Control Module U Code List .
- Refer to Data Link References to determine which data communication bus the non communicating device is on.
- If the device is on Gateway Expansion High Speed GMLAN bus
Refer to Scan Tool Does Not Communicate with Gateway Expansion High Speed GMLAN Device to diagnose that device.
- If the device is on Gateway Isolated High Speed GMLAN bus
Refer to Scan Tool Does Not Communicate with Gateway Isolated High Speed GMLAN Device to diagnose that device.
- If the device is on Gateway Isolated Low Speed GMLAN bus
Refer to Scan Tool Does Not Communicate with Gateway Isolated Low Speed GMLAN Device to diagnose that device.
- Go to next step: If the device is not on Gateway Expansion High Speed GMLAN bus, Gateway Isolated High Speed GMLAN bus, and Gateway Isolated Low Speed GMLAN bus
- If the device is on Gateway Expansion High Speed GMLAN bus
- Refer to Circuit/System Testing.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.