P0974
Shift Solenoid A Control Circuit HighP0974 is a generic OBD-II powertrain diagnostic trouble code: Shift Solenoid A Control Circuit High. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0974 means
P0974 is set when the Transmission Control Module (TCM) detects an abnormally high voltage on the Shift Solenoid "A" (Clutch Pressure Control Solenoid A) control circuit. In a normal PWM-driven solenoid circuit the TCM low-side driver pulls the solenoid circuit to near ground when energised; a "high" circuit fault means the driver sees voltage on the circuit that it did not command — typically caused by a short-to-battery (12 V) on the control wire, a shorted low-side driver inside the TCM, or an internal solenoid failure that keeps the circuit clamped high.
The practical effect is the same as P0973: the TCM can no longer modulate solenoid A pressure, disables the circuit, and may engage fail-safe mode. However, a short-to-voltage fault often points to a different wiring location than a short-to-ground, so wiring harness inspection should specifically look for contact between the solenoid control wire and any 12 V supply wire such as the ignition feed or the solenoid pack power feed.
P0974 is closely related to P0973 and both may be set simultaneously on platforms where the TCM performs bidirectional circuit monitoring. Addressing the root wiring or solenoid fault will resolve both codes. Common platforms include GM 6L80/6T70, Ford 6F35/6R80, ZF 6HP/8HP, and Mercedes 722.6/722.9.
Common causes
Most-frequently reported root causes when P0974 is logged.
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1
Short-to-battery voltage on the solenoid A control wire, typically where the harness contacts a 12 V supply or ignition feed.
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2
Shorted low-side driver inside the TCM causing the control line to be held at high voltage regardless of commanded state.
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3
Internally shorted solenoid coil that clamps the circuit high and prevents normal PWM modulation.
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4
Corroded or bridged connector terminals allowing the control pin to contact an adjacent power pin.
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5
Damaged wiring insulation from heat, chafing, or animal activity creating an unintended contact with a 12 V circuit.
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6
Incorrect harness routing after a prior repair placing the transmission harness adjacent to a live power line.
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7
Contaminated or degraded transmission fluid contributing to solenoid valve sticking alongside the electrical fault.
Symptoms drivers notice
How to diagnose P0974
A typical diagnostic flow when this code is present.
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1
Retrieve all stored DTCs with a scan tool and note whether P0973 is also present, as simultaneous Low and High codes point toward a TCM driver fault rather than a simple wire short.
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2
Inspect the transmission wiring harness for insulation damage, heat exposure, or contact between the solenoid A control wire and any power-supply wiring.
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3
Disconnect the transmission harness connector and measure voltage on the solenoid A control terminal with the ignition on — any reading above 1 V indicates an external short-to-power.
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4
With the connector still unplugged, measure resistance of the solenoid A circuit from the TCM side to ground; a very low reading confirms a TCM driver short.
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5
Inspect all connector pins for bridging, corrosion, or bent terminals that could create cross-circuit contact with adjacent power pins.
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6
Check transmission fluid level and condition; replace if burnt or contaminated.
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7
If external wiring is fault-free, suspect the TCM driver stage or an internally shorted solenoid and perform a bench resistance test on the solenoid before proceeding to TCM replacement.
Related powertrain codes
Frequently asked questions
What is the difference between P0973 (Low) and P0974 (High)?
P0973 indicates the circuit voltage is below the minimum threshold — caused by an open circuit, short to ground, or open solenoid coil. P0974 indicates the circuit voltage is above the maximum threshold — caused by a short to battery voltage or a shorted TCM driver. Both prevent proper solenoid control but point to different fault locations in the circuit.
Can P0974 damage the TCM?
A sustained short-to-voltage on a solenoid driver output can overheat and damage the TCM's internal driver transistor. If the code resets immediately after clearing, disconnect the solenoid harness to protect the TCM and diagnose the external circuit before powering the system again.
Will replacing the solenoid fix P0974?
Possibly, if the solenoid itself is internally shorted. However, an external wiring short-to-battery is far more common and replacing the solenoid will not fix it. Always perform circuit testing with a DVOM before changing parts.
Is limp mode engaged every time P0974 is set?
Most modern TCMs enter limp mode (fixed single gear) whenever a pressure-control solenoid circuit fault is confirmed, as a safety measure to prevent hydraulic pressure runaway. The exact fail-safe strategy varies by manufacturer — some allow limited manual gear selection while others lock the transmission entirely.
Disabling P0974 in software
RaceTune can permanently disable P0974 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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