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.
Test Procedure
- TD1 DIAGNOSTIC TROUBLE CODE (DTC) P0A18: VERIFY THE CONCERN IS PRESENT
- Record and clear all continuous memory DTCs.
- Retrieve the PCM continuous memory DTCs.
Is DTC P0A18 present?
Yes No GO to TD2. GO to TD7. - TD2 CHECK THE TMAC CIRCUIT FOR AN OPEN CIRCUIT IN THE HARNESS
- Ignition OFF.
- PCM connector disconnected.
- Transaxle Assembly-B connector disconnected.
- Measure the resistance between:
RESISTANCE REFERENCE CHART(+) PCM Connector, Harness Side (-) Transaxle Assembly-B Connector, Harness Side TMAC - Pin C6 TMAC - Pin 4 Is the resistance less than 5 ohms?
Yes No GO to TD3. REPAIR the circuit.
Clear the PCM DTCs. REPEAT the self-test. - TD3 CHECK THE TMAC CIRCUIT FOR A SHORT TO VOLTAGE IN THE HARNESS
- Ignition ON, engine OFF.
- Measure the voltage between:
VOLTAGE REFERENCE CHART(+) PCM Connector, Harness Side (-) Vehicle Battery TMAC - Pin C6 Negative terminal Is the voltage less than 1 V?
Yes No GO to TD4. REPAIR the circuit.
Clear the PCM DTCs. REPEAT the self-test. - TD4 CHECK THE TMAC CIRCUIT FOR A SHORT TO GROUND IN THE HARNESS
- Ignition OFF.
- Measure the resistance between:
RESISTANCE REFERENCE CHART(+) PCM Connector, Harness Side (-) Vehicle Battery TMAC - Pin C6 Negative terminal Is the resistance greater than 10K ohms?
Yes No GO to TD5. REPAIR the circuit.
Clear the PCM DTCs. REPEAT the self-test. - TD5 CHECK FOR THE TMAC CIRCUIT SHORTED TO SIGNALS IN THE SAME HARNESS
- Measure the resistance between:
RESISTANCE REFERENCE CHART(+) Transaxle Assembly-B Connector, Harness Side (-) Transaxle Assembly-B Connector, Harness Side TMAC - Pin 4 ISDN2 - Pin 7 TMAC - Pin 4 GMSDN - Pin 5 TMAC - Pin 4 CTO - Pin 1 TMAC - Pin 4 TGAC - Pin 9 Are the resistances greater than 10K ohms?
Yes No GO to TD6. REPAIR the circuit.
Clear the PCM DTCs. REPEAT the self-test. - TD6 TMAC FUNCTIONAL TEST
- PCM connector connected.
- Transaxle Assembly-B connector connected.
- Isolate the TMAC pin from the Transaxle-B connector.
- Connect a 5 amp fused jumper wire between the following:CONNECTOR PINS REFERENCE CHART
Point A Transaxle Assembly-B Connector, Harness Side Point B Transaxle Assembly-B Connector, Harness Side TMAC - Pin 4 TGAC - Pin 9 - Ignition ON, engine running.
Does the engine start now?
Yes No INSTALL a new transaxle assembly. REFER to the ELECTRONICALLY CONTROLLED CONTINUOUSLY VARIABLE TRANSMISSION (ECVT) GO to TD8. - TD7 CHECK THE TMAC CIRCUIT FOR AN INTERMITTENT CONCERN
- Ignition ON, engine OFF.
- Access the PCM and monitor the MTQ (TORQUE) PID.
- Carefully wiggle all accessible wiring and connectors associated with the circuit and look for a change in the PID state.
Is a concern present during the wiggle test?
Yes No REPAIR as necessary.
Clear the PCM DTCs. REPEAT the self-test.GO to PINPOINT TEST Z . - TD8 CHECK FOR CORRECT PCM OPERATION
- Disconnect all the PCM connectors.
- Visually inspect for:
- pushed out pins
- corrosion
- Connect all the PCM connectors and make sure they seat correctly.
- Carry out the PCM self-test.
- Verify the concern is still present.
Is the concern still present?
Yes No INSTALL a new PCM.
REFER to FLASH ELECTRICALLY ERASABLE PROGRAMMABLE READ ONLY MEMORY (EEPROM) .The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.
NO RELATED
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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.