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DTC codes / P08xx · Transmission / P08C8

P08C8Pressure Control Solenoid M Control Circuit/Open

P08C8 indicates that the transmission control module (TCM) has detected an open circuit or excessive resistance in the electrical path for pressure control solenoid M, which is used to regulate hydraulic pressure inside the transmission. The TCM monitors the solenoid's command circuit and flags the code when the expected current or voltage is not present, often resulting in degraded shift quality or a default limp mode.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaTransmission

Symptoms you may notice

  • Illumination of the check engine light or transmission warning light, often with no other noticeable symptoms
  • Harsh or delayed gear shifts, especially when the transmission is cold
  • Transmission stuck in a single gear or limp mode with reduced power
  • Slipping or flaring during acceleration or when changing gears
  • Erratic shift points or failure to downshift when passing
  • Increased engine RPM at highway speeds due to torque converter clutch not engaging

Common causes, most likely first

  1. Damaged or disconnected wiring harness at the solenoid connector or along the transmission case
  2. Corroded, loose, or pushed-back terminals inside the solenoid electrical connector
  3. Open winding inside pressure control solenoid M itself
  4. Failed transmission control module (TCM) driver circuit for solenoid M
  5. Internal transmission damage causing debris to block solenoid operation or damage the solenoid
  6. Poor ground connection for the transmission or TCM, leading to erratic solenoid control
  7. Aftermarket or incorrect solenoid replacement that does not meet electrical specifications

How to diagnose and fix it

  1. Connect a scan tool and verify P08C8 is current or history, then check for related transmission codes and freeze-frame data
  2. Inspect the solenoid M electrical connector and harness for damage, corrosion, or loose pins, and repair as needed
  3. Measure resistance of solenoid M at the transmission connector and compare to manufacturer specification to rule out an open coil
  4. Check continuity and voltage drop on the control circuit from the TCM to the solenoid, looking for opens or high resistance
  5. Test the TCM driver output with a bidirectional scan tool or oscilloscope to confirm the TCM is commanding the solenoid correctly
  6. If electrical tests pass, remove the transmission pan and inspect solenoid M for debris, damage, or sticking, replacing it if necessary
  7. After repair, clear codes and perform a relearn or adaptation drive cycle to verify the transmission shifts correctly and the code does not return

Hidden causes of P08C8 you should not overlook

  • A loose or corroded ground strap between the transmission and chassis can cause intermittent open-circuit codes for multiple solenoids, not just M, so always check grounds before condemning the solenoid.
  • The TCM may set P08C8 as a secondary code when the transmission fluid is low or severely degraded, because the solenoid cannot maintain commanded pressure and the TCM interprets the resulting electrical signature as an open circuit.
  • Some vehicles use a single shared power feed for several pressure control solenoids; a fault in that feed can set codes for multiple solenoids, so look for companion codes that point to a common circuit rather than replacing each solenoid individually.
  • After replacing a solenoid or repairing wiring, many TCMs require a adaptive learning reset or a specific drive cycle to relearn clutch volumes; skipping this step can leave the transmission shifting poorly and make you think the repair failed.
  • A faulty ignition switch or power relay that briefly drops voltage to the TCM can cause a stored P08C8 without any hard wiring fault, so check for intermittent power loss symptoms such as other modules setting communication codes.

Can I keep driving with P08C8?

You can usually drive the vehicle to a repair shop if the transmission is not in limp mode, but avoid aggressive acceleration or heavy towing because the transmission may not regulate pressure correctly and could suffer internal damage. If the vehicle is stuck in a single gear or the warning light is flashing, stop driving and have it towed to prevent further damage.

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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