Failed pressure control solenoid C inside the transmission valve body, with an open or shorted coil winding; Damaged or chafed wiring harness between the TCM and the transmission connector, often near the bellhousing or along the gearbox casing; Corroded, oil-contaminated, or loose electrical connector at the transmission pass-through or valve body plug; Internal valve body fault such as a stuck valve or worn bore that mechanically loads the solenoid and causes an electrical signature the TCM interprets as a circuit fault; Low or degraded transmission fluid causing poor solenoid operation and secondary electrical symptoms; TCM software or internal driver fault, though this is less common than wiring or solenoid failure

DTC codes / BMW codes / P1738

P1738 · BMWPressure Control Solenoid C Electrical

Q: What does code P1738 mean?

Pressure Control Solenoid C Electrical. P1738 on a BMW indicates that the transmission control module (TCM) has detected an electrical fault in the circuit for pressure control solenoid C, which is one of the electro-hydraulic valves that regulates clutch apply pressure inside the automatic gearbox. The TCM monitors the solenoid's electrical current and voltage and sets this code when the measured values fall outside the expected range, pointing to an open circuit, short to ground, short to power, or a failed solenoid coil. This is an electrical fault, not a hydraulic or mechanical fault, so diagnosis should focus on wiring, connectors, and the solenoid itself before condemning the transmission.

P1738 on a BMW indicates that the transmission control module (TCM) has detected an electrical fault in the circuit for pressure control solenoid C, which is one of the electro-hydraulic valves that regulates clutch apply pressure inside the automatic gearbox. The TCM monitors the solenoid's electrical current and voltage and sets this code when the measured values fall outside the expected range, pointing to an open circuit, short to ground, short to power, or a failed solenoid coil. This is an electrical fault, not a hydraulic or mechanical fault, so diagnosis should focus on wiring, connectors, and the solenoid itself before condemning the transmission.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyProfessional

AreaTransmission

Symptoms you may notice

Illumination of the transmission malfunction warning light or the check engine light, often with a message in the iDrive display
Harsh or delayed gear engagements, especially when selecting Drive or Reverse from a stop
Transmission stuck in a limp-home mode with a single fixed gear or restricted shift pattern
Erratic or slipping shifts as the TCM loses the ability to regulate clutch pressure precisely
Sometimes no symptoms besides the warning light, particularly if the fault is intermittent and the TCM has not yet defaulted to a safe mode

Common causes, most likely first

Failed pressure control solenoid C inside the transmission valve body, with an open or shorted coil winding
Damaged or chafed wiring harness between the TCM and the transmission connector, often near the bellhousing or along the gearbox casing
Corroded, oil-contaminated, or loose electrical connector at the transmission pass-through or valve body plug
Internal valve body fault such as a stuck valve or worn bore that mechanically loads the solenoid and causes an electrical signature the TCM interprets as a circuit fault
Low or degraded transmission fluid causing poor solenoid operation and secondary electrical symptoms
TCM software or internal driver fault, though this is less common than wiring or solenoid failure

How to diagnose and fix it

Scan all modules with a BMW-capable diagnostic tool and record the freeze-frame data and any accompanying transmission codes before clearing anything
Inspect the transmission wiring harness and connectors for chafing, corrosion, oil ingress, and loose pins, repairing any damage found
Measure the resistance of pressure control solenoid C at the transmission connector and compare it with the BMW specification for the fitted gearbox
Check the solenoid circuit for shorts to ground and shorts to power with a multimeter, isolating the TCM if necessary
If electrical values are within specification, remove the valve body and test the solenoid directly, replacing it if the coil is out of tolerance
After repair, clear the fault memory, perform the transmission adaptation reset with the diagnostic tool, and road-test through all gears to confirm the code does not return

What BMW technicians check before replacing a solenoid

A chafed harness section behind the transmission bellhousing or near the exhaust heat shield is a frequent cause of P1738 on BMW models, and it can mimic a failed solenoid perfectly.
Oil contamination at the transmission pass-through connector can create intermittent resistance changes that set the code only when the gearbox is hot, so always test the circuit both cold and at operating temperature.
A mechanically sticking valve in the valve body can load the solenoid and produce an electrical fault code even when the solenoid coil itself tests good, so a resistance check alone is not conclusive.
Replacing the solenoid without resetting and relearning the transmission adaptations often leaves the gearbox shifting poorly, which owners then misread as a failed repair.
P1738 can be stored alongside pressure control codes for other solenoids when the root cause is a shared ground or power feed in the transmission harness, so always check the common circuit before condemning multiple solenoids.

Can I keep driving with P1738?

You can usually drive the car to a workshop if the transmission still engages gears and the warning light is steady, but avoid heavy acceleration, towing, and long trips because limp-home mode can engage without warning. If the gearbox slips, refuses to engage a gear, or the warning light flashes, stop driving and arrange recovery to prevent internal transmission damage.

Tools that help

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