Diagnostic guide for U0155

Diagnostic Guide for U0155 - F-CAN Malfunction

The U0155 code indicates a communication issue between the Powertrain Control Module (PCM) and the Gauge Control Module via the F-CAN lines. The goal of this diagnostic guide is to identify the root cause of the communication failure and resolve it to restore proper functionality.

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Difficulty

Intermediate

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Estimated Time

30-60 Minutes

Estimated Diagnostic Cost

$0-$100

Typical shop charge to perform this diagnostic process. Repair parts and labor are not included.

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Tools Needed

OBDII scanner, multimeter, wiring diagram, basic hand tools

Safety Notes

Ensure the vehicle is in park with the engine off before starting. Be cautious of moving parts and hot surfaces when inspecting the engine compartment.

Step 1

Reset the Battery

Instruction Disconnect the negative battery cable for 5 seconds, then reconnect it.

Expected result The engine light may turn off if the issue was temporary.

If Pass If the DTC does not return, the issue may have been a glitch. Monitor the vehicle for any reoccurrence.

If Fail If the DTC returns, proceed to the next step to further diagnose the issue.

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Step 2

Check for Additional Codes

Instruction Use an OBDII scanner to check for any additional DTCs that may provide more context.

Expected result A list of DTCs, including U0155 and any other related codes.

If Pass If other codes are present, investigate those first as they may lead to the root cause.

If Fail If no additional codes are found, proceed to inspect the wiring and connections.

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Step 3

Inspect the Gauge Control Module Connections

Instruction Visually inspect the wiring and connectors at the Gauge Control Module for signs of damage, corrosion, or loose connections.

Expected result Wiring and connectors should appear intact and securely connected.

If Pass If the connections are good, proceed to test the F-CAN lines.

If Fail If any damage or poor connections are found, repair or replace as necessary and retest.

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Step 4

Test the F-CAN Signal Lines

Instruction Using a multimeter, check the resistance and voltage on the F-CAN lines (CANH and CANL) while the vehicle is in the ON position.

Expected result Resistance should be within specifications, and voltage should show pulsing signals.

If Pass If signals are present and within specifications, the issue may lie within the PCM.

If Fail If signals are absent or out of specification, inspect the wiring for shorts or opens.

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Step 5

Check the Powertrain Control Module (PCM)

Instruction Inspect the PCM for any signs of damage or corrosion, and ensure all connections are secure.

Expected result The PCM should be intact with secure connections.

If Pass If the PCM appears fine, further diagnostics may be needed to test its functionality.

If Fail If damage is found, consider replacing the PCM or consulting a professional for further testing.

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Coddy can help with this step only. Tell me what you tested or what result you got.