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.
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HOMESERVICE MANUALSCHEVROLET2025TAHOE COMMERCIAL, 4WDREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMDATA COMMUNICATIONS - DIAGNOSTIC INFORMATION AND PROCEDURES (1 OF 4)DIAGNOSTIC INFORMATION AND PROCEDURESDTC B1A1D (K56 SERIAL DATA GATEWAY MODULE)CIRCUIT/SYSTEM TESTING
2025 Chevrolet Tahoe Commercial, 4WD
Circuit/System Testing
2025 Chevrolet Tahoe Commercial, 4WDSECTION Circuit/System Testing
NOTE:
Use the schematics and connector end views to identify the control module's ground, B+, ignition, and Ethernet serial data circuit terminals.
- Ignition/Vehicle OFF, disconnect the harness connectors at the K124 Image Processing Module.
- Verify a test lamp illuminates between each of the ground circuit terminals and B+.
- If the test lamp does not illuminate
Repair the open/high resistance in the ground circuit or ground connection.
- Go to next step: If the test lamp illuminates
- If the test lamp does not illuminate
- Ignition ON/Vehicle In Service Mode.
- If equipped, verify a test lamp illuminates between each of the B+ circuit terminals and ground.
- If the test lamp does not illuminate and the circuit fuse is good
- Test for an open/high resistance in the B+ circuit.
- If an open/high resistance is found, repair the fault on the circuit.
- Go to next step: If an open/high resistance is not found
- Verify the fuse is not open and there is voltage at the fuse.
- If the test lamp does not illuminate and the circuit fuse is open
- Test for a short to ground in the B+ circuit.
- If a short to ground is found, repair the fault in the circuit.
- Go to next step: If a short to ground is not found
- Replace the K124 Image Processing Module.
- Go to next step: If the test lamp illuminates
- If equipped, verify a test lamp illuminates between each of the ignition circuit terminals, which has a fuse in the circuit, and ground.
- If the test lamp does not illuminate and the circuit fuse is good
- Test for an open/high resistance in the ignition circuit.
- If an open/high resistance is found, repair the fault in the circuit.
- Go to next step: If an open/high resistance is not found
- Verify the fuse is not open and there is voltage at the fuse.
- If the test lamp does not illuminate and the circuit fuse is open
- Test for a short to ground in the ignition circuit.
- If a short to ground is found, repair the fault in the circuit.
- Go to next step: If a short to ground is not found
- Replace the K124 Image Processing Module.
- Go to next step: If the test lamp illuminates
- Ignition/Vehicle OFF, disconnect the harness connectors at the K56 Serial Data Gateway Module.
- Ignition ON/Vehicle In Service Mode.
- Test for less than 1 V between each of the Ethernet bus 3 circuit terminals and ground.
- If 1 V or greater
Repair the short to voltage in the circuit.
- Go to next step: If less than 1 V
- If 1 V or greater
- Ignition/Vehicle OFF, all access doors closed, all vehicle systems OFF, and all keys at least 3 m (9.8 ft) away from vehicle. It may take up to 10 min for all vehicle systems to power down.
- Test for infinite resistance between each of the Ethernet bus 3 circuit terminals and ground.
- If less than infinite resistance
Repair the short to ground in the circuit.
- Go to next step: If infinite resistance
- If less than infinite resistance
- Test for infinite resistance between the pair of the Ethernet bus 3 circuit terminals.
- If less than infinite resistance
Repair the short together in the circuits.
- Go to next step: If infinite resistance
- If less than infinite resistance
- Test for less than 2 Ω in each of the Ethernet bus 3 circuits end to end.
- If 2 Ω or greater
Repair the open/high resistance in the circuit.
- Go to next step: If less than 2 Ω
- If 2 Ω or greater
- Inspect both harness and component connectors for contamination, corrosion, and terminal tension.
- Reconnect the harness connectors at the K124 Image Processing Module and the K56 Serial Data Gateway Module.
- Ignition ON/Vehicle In Service Mode.
- Verify DTC B1A1D is not set.
- If the DTC is set
- Replace the K124 Image Processing Module.
- Ignition ON/Vehicle In Service Mode.
- Verify DTC B1A1D does not set again.
- If the DTC sets, replace the K56 Serial Data Gateway Module.
- Go to next step: If the DTC does not set
- All OK.
- Go to next step: If the DTC is not set
- A fault is currently not present and may be an intermittent condition.
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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.