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DTC codes / P08xx · Transmission / P0886

P0886TCM Power Relay Control Circuit Low

P0886 means the transmission control module (TCM) has detected that the voltage on the control circuit for its power relay is lower than expected when the relay should be energized. The TCM monitors this circuit and sets the code when the signal wire shows a short to ground, an open circuit, or excessive resistance that prevents proper relay operation.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • The check engine light or transmission warning light illuminates on the dashboard.
  • The transmission may enter limp mode, staying in a single gear or refusing to shift.
  • Harsh or delayed shifts, or a complete loss of automatic shifting.
  • The engine may crank but fail to start if the TCM power relay also supplies power to other critical circuits.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.

Common causes, most likely first

  1. A faulty TCM power relay that has failed internally or has burned contacts.
  2. A short to ground in the control circuit wiring between the TCM and the relay.
  3. Corroded, loose, or damaged connectors at the TCM, relay, or inline harness connectors.
  4. An open circuit or high resistance in the control wire, often due to a broken wire or poor splice.
  5. A defective TCM driver circuit that cannot pull the relay control line low.
  6. Blown fuse or poor ground connection supplying power to the relay coil or TCM.
  7. Water intrusion or chafed wiring causing intermittent shorts in the harness.

How to diagnose and fix it

  1. Verify the battery is fully charged and check all fuses related to the TCM and relay; replace any blown fuse and retest.
  2. Inspect the TCM power relay and its socket for corrosion, loose terminals, or burn marks; swap with a known-good relay of the same part number and clear the code.
  3. Disconnect the TCM and the relay, then use a multimeter to check the control circuit for a short to ground and for continuity; repair any damaged wire or connector.
  4. Check the relay coil resistance and confirm it matches the manufacturer's specification; replace the relay if out of range.
  5. Backprobe the TCM connector and measure voltage on the control circuit while commanding the relay on with a scan tool; if voltage stays high, suspect the TCM driver.
  6. Perform a voltage drop test on the ground circuit for the TCM and relay; clean or repair any excessive resistance.
  7. If all wiring and the relay test good, substitute a known-good TCM and retest; replace the TCM only after confirming the driver circuit is faulty.

Before you replace the TCM

  • A loose or corroded battery terminal can cause this code because the TCM sees a voltage drop on its power feed and misinterprets it as a relay control circuit fault.
  • Many technicians replace the TCM when the real problem is a chafed wire behind the transmission bell housing or near the exhaust, so always perform a wiggle test on the harness while monitoring the circuit.
  • The TCM power relay often shares its control circuit with other relays or modules, so a short in a different circuit can set P0886 even though the transmission relay itself is fine.
  • Intermittent P0886 codes that appear only in cold or wet weather usually point to a wiring harness issue rather than a failed relay or TCM.
  • A weak battery or failing alternator can set P0886 because the TCM may not receive stable voltage during cranking, causing it to log a low circuit fault.

Can I keep driving with P0886?

If the transmission is in limp mode or shifting erratically, avoid highway driving and have the vehicle towed or driven only to a nearby repair shop. If the only symptom is the warning light and the car drives normally, you can drive cautiously to a workshop, but do not ignore the code because it may worsen and leave you stranded.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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