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DTC codes / P09xx · Transmission / P0974

P0974Shift Solenoid 'A' Control Circuit High

P0974 means the transmission control module (TCM) has detected an abnormally high voltage on the control circuit for shift solenoid 'A', which is the solenoid that controls fluid pressure for one of the forward gear shifts. The TCM commands the solenoid on or off and monitors the circuit; a high voltage reading tells it the circuit is open, shorted to power, or the solenoid coil is not drawing the expected current.

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 default to a limp mode, staying in one gear or only reverse.
  • Harsh or delayed shifts, or a refusal to shift into certain gears.
  • The engine may rev higher than normal at a given road speed because a gear is missing.
  • Often no symptoms besides the warning light, especially if the fault is intermittent.

Common causes, most likely first

  1. A failed shift solenoid 'A' with an open internal coil or damaged connector.
  2. Corroded, loose, or damaged wiring or connector pins in the solenoid circuit.
  3. A short to voltage on the signal wire between the TCM and the solenoid.
  4. A faulty transmission control module (TCM) or internal driver circuit.
  5. Contaminated transmission fluid or a blocked solenoid screen causing abnormal circuit feedback.
  6. A poor ground connection for the solenoid or TCM.

How to diagnose and fix it

  1. Scan all modules and record freeze-frame data to confirm P0974 is active and not a history code.
  2. Inspect the solenoid 'A' connector and harness for corrosion, loose pins, or chafed wires.
  3. Measure resistance across solenoid 'A' and compare to the manufacturer's specification.
  4. Check for short to voltage on the signal wire with the key on and the TCM disconnected.
  5. Test the TCM ground and power feeds, and verify the TCM driver output with a lab scope if available.
  6. If the circuit tests good, replace shift solenoid 'A' and perform a transmission fluid service.
  7. Clear codes and road test through all gears to confirm the repair and that no new codes set.

What the high-voltage reading really means

  • A high voltage on a solenoid control circuit usually means the circuit is open, not shorted, because the TCM pulls the low side down and sees battery voltage when the coil cannot complete the path.
  • Many technicians replace the solenoid first and later find a corroded connector pin or a chafed wire in the harness, so always inspect the wiring before condemning the part.
  • Intermittent P0974 codes often appear only when the transmission is hot or after a bump, which points to a loose connection rather than a failed solenoid.
  • A faulty TCM can set this code by misreporting voltage, but that is rare; confirm the circuit with a multimeter before replacing the module.
  • Low or contaminated transmission fluid can cause solenoid performance codes that mimic circuit faults, so check fluid condition and level as part of the diagnosis.

Can I keep driving with P0974?

You can usually drive the vehicle to a repair shop if the transmission still shifts, but avoid heavy acceleration and highway speeds because limp mode may engage without warning. If the transmission is stuck in one gear or will not engage drive, stop driving and have it towed to prevent further damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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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