Fix C0242: Mechanic’s Solutions That WORKED!

The C0242: PCM Indicated TCS Malfunction indicates a communication issue between the Powertrain Control Module (PCM) and the Electronic Brake Control Module (EBCM), specifically concerning the Traction Control System (TCS).

This code suggests that the PCM has detected a problem that prevents it from properly managing traction control, a feature crucial for maintaining vehicle stability. Such a situation can lead to symptoms like poor vehicle performance, illuminated warning lights, and activation of safety systems at inappropriate times.

C0242 quick overview

Meaning	C0242: PCM Indicated Traction Control System Malfunction
Is it serious?	Yes, as it affects the vehicle’s traction control and potentially its overall safety and performance.
Possible causes	– Faulty communication between PCM and EBCM – Lean condition in the engine affecting TCS functionality – Low brake fluid levels causing TCS alerts – Electrical issues within the EBCM
How to diagnose?	Address any engine-related codes (e.g., lean conditions) that might impact TCS functionality. Check brake fluid levels and top up if necessary. Inspect the wiring and connectors between the PCM and EBCM for damage or corrosion. Consider the condition of the EBCM itself, including power supply and ground connections. Use a specialized scanner to pinpoint communication issues and verify repair effectiveness.

How to fix C0242 – learn from mechanics

I looked into C0242 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: GMC C0242

Vehicle information 2013 GMC Acadia Denali 3.6L

Issue + repair history

• Complaints: vehicle running poorly, check engine light on, traction control light on, multiple codes present.
• DTCs: P0171, P0174, P0089 stored in ECM, along with TSBs 00-55-22-8c and 00-55-00-C6 (unlocated), and main concern DTC C0242 stored in EBCM.
• C0242 indicates a communication issue between EBCM and ECM regarding traction control.
• Lean codes (P0171, P0174) triggered by Power Brake Booster Solenoid Vacuum Supply failing smoke test.
• Even after blocking off the vacuum hose to the booster, C0242 persists as a hard code, along with other false codes.
• Ohmed out serial data lines, checked power and ground circuits to ECM, ENCM, and BCM, all found good.

Other OBD2 Codes + Test Results

• P0171: System Too Lean (Bank 1)
• P0174: System Too Lean (Bank 2)
• P0089: Fuel Pressure Regulator 1 Performance

Mechanic suggestions

• Check if EBCM is resetting and requesting the code to be cleared.
• Investigate further into the P0089 fuel pressure regulator issue before addressing C0242.
• Verify fuel pressure within specified range, inspect high pressure fuel pump assembly, and test circuits of the FRP solenoid for high resistance.
• Address lean condition (P0171, P0174) first, as it may be causing other issues.
• Perform additional checks such as inspecting for brake fluid in the booster and verifying fuel delivery.

Final fix

• Replaced Brake Booster Vacuum Pump to address lean codes.
• Replaced PCM to address code C0242

Case #2: Chevrolet C0242

Vehicle information 2006 Chevrolet Impala LS 3.5L

Issue + repair history

• Complaints: ABS activates causing traction control lamp to illuminate momentarily and vehicle to shudder during mid-range cruise conditions.
• DTC C0242 stored, indicating ECM indicated TCS malfunction.
• OTC scan tool gave “ABS module comm lost” message.
• No related DTCs found upon follow-up diagnostics.

Other OBD2 Codes + Test Results N/A

Mechanic suggestions

• Perform a physical examination and general check-up of the vehicle.
• Check wheel speed sensors for any weaknesses by “lab scoping” each sensor and comparing waveform patterns.
• Consider using a different scanner to retrieve more accurate diagnostic information.
• Verify tire diameter and inspect speed sensors for erratic spikes causing traction control activation.

Final fix

• Low brake fluid level was identified as the cause of the problem.
• Despite other diagnostic efforts, topping off the brake fluid reservoir resolved the issue, eliminating ABS activation and shuddering during mid-range cruise conditions.

Case #3: GMC C0242

Vehicle information 1999 GMC Safari SL 4.3L

Issue + repair history

• ABS light comes on as soon as the vehicle goes above 3mph and stays on.
• Diagnostic Trouble Code (DTC) C0242 stored, indicating EBCM control valve circuit issue.
• Diagnostics suggested checking power and ground connector at the EBCM, which tested good.
• Next step according to diagnostics is to replace the EBCM.
• Customer declined replacement and opted to drive with the light on.

Other OBD2 Codes + Test Results N/A

Mechanic suggestions

• Check for power loss to the EBCM and ensure terminals aren’t corroded.
• Consider making a jumper wire directly to the EBCM to test if the code still sets.
• Replace the EBCM, especially if it’s the unit with the ABS control module mounted to the top of the pump.
• Label brake lines when replacing the EBCM to avoid connecting them incorrectly.
• Verify sensor outputs and power and grounds to the EBCM before further diagnosis.
• Check ignition voltage wires for cuts or damage.
• Inspect power pigtail wires for corrosion.
• Run ABS automated bleed test multiple times and clear codes to retest.
• Consider the possibility of logic lock in the module.
• Replace the entire ABS unit due to potential valve issues.

Final fix

• Replacing the EBCM fixed the issue.