P0748

Pressure Control Solenoid A Electrical

P0748 is a generic OBD-II powertrain diagnostic trouble code: Pressure Control Solenoid A Electrical. 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.

Code
P0748
Group
Powertrain
System
Powertrain
Severity
high
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What P0748 means

P0748 is stored when the PCM or TCM detects an electrical fault in the Pressure Control Solenoid 'A' (PCS-A) circuit. The pressure control solenoid is a variable-force PWM solenoid that regulates line pressure throughout the transmission; by varying current through the solenoid the TCM adjusts mainline hydraulic pressure to suit current driving conditions—light pressure for smooth part-throttle shifts, high pressure for firm full-throttle engagement and towing. The 'A' designation identifies the primary or first solenoid in a multi-solenoid assembly; its exact physical location varies by make and model.

The fault is exclusively electrical: the module has commanded a specific duty cycle to the solenoid but the measured circuit response—voltage drop, current draw, or feedback signal—is outside specification. This typically means an open circuit (broken wire or corroded connector), a short to ground, or a short to voltage somewhere in the circuit between the TCM output driver and the solenoid winding. An internally failed solenoid with an open or shorted coil will produce the same fault as a wiring issue, and a multimeter test of solenoid resistance is the fastest way to differentiate the two.

Because PCS-A directly governs mainline pressure, an electrical failure that disables it forces the TCM into a default high-pressure mode (fail-safe). Shifts become noticeably harsh and abrupt as the transmission applies clutch packs with maximum hydraulic force regardless of throttle position. This protects clutch durability but significantly degrades shift quality and driver comfort.

Neglected transmission fluid is a contributing factor in many cases: contaminated fluid accelerates solenoid winding corrosion from the inside while also increasing circuit resistance. Fluid condition should always be inspected as part of this diagnosis. TCM internal driver failure is uncommon but should be considered when solenoid, wiring, and connectors all test within specification.

Common causes

Most-frequently reported root causes when P0748 is logged.

  • 1
    Open circuit in PCS-A wiring (broken or corroded wire)
  • 2
    Short to ground in the pressure control solenoid circuit
  • 3
    Corroded or damaged solenoid harness connector
  • 4
    Failed pressure control solenoid (open or shorted winding)
  • 5
    Short to battery voltage in PCS-A circuit
  • 6
    Contaminated transmission fluid degrading solenoid internals
  • 7
    Low transmission fluid causing pressure regulation errors
  • 8
    Faulty TCM internal solenoid driver (rare)

Symptoms drivers notice

Check engine light illuminated
Harsh, abrupt, or banging gear shifts across all gears
Transmission slipping or delayed engagement
Transmission stuck in limp/fail-safe mode
Engine stalling at low speed or when stopping
Reduced fuel economy
Transmission overheating

How to diagnose P0748

A typical diagnostic flow when this code is present.

  1. 1
    Connect an OBD-II scanner and record all stored codes and freeze-frame data; note whether other pressure or solenoid codes are present
  2. 2
    Check transmission fluid level and inspect for burnt odour, dark colour, or contamination
  3. 3
    Locate the PCS-A connector at the transmission; visually inspect for corrosion, damaged pins, or moisture
  4. 4
    With the connector unplugged, measure solenoid winding resistance; compare to OEM specification (commonly 3–10 Ω for variable-force solenoids); open or shorted reading indicates solenoid failure
  5. 5
    Check supply voltage and ground integrity at the solenoid connector with key-on engine-off
  6. 6
    Perform continuity and short-to-ground tests on the full wiring harness between the solenoid and TCM
  7. 7
    Using a scan tool with live data, command PCS-A duty cycle and monitor current response; absence of current change with commanded duty confirms wiring or solenoid fault
  8. 8
    If all external components test good, evaluate TCM for internal driver failure or available software updates

Related powertrain codes

Frequently asked questions

What does 'Solenoid A' mean—which solenoid is it exactly?

The SAE designation 'A' identifies the first or primary pressure control solenoid in the transmission's hydraulic circuit. Its exact location depends on the vehicle manufacturer; your workshop manual or wiring diagram will show the connector location and circuit routing for your specific model.

Why do shifts become harsh when P0748 is active?

When the TCM loses control of the pressure solenoid it defaults to maximum line pressure to protect the clutch packs from slipping. Maximum pressure produces firm, abrupt shifts rather than smoothly modulated ones—this is intentional fail-safe behaviour.

Can dirty transmission fluid cause P0748?

Yes. Contaminated fluid can corrode solenoid windings from inside, increase internal resistance, and trigger the out-of-range electrical reading. A fluid service is a sensible first step and may resolve the fault if the solenoid is not yet mechanically failed.

Is P0748 the same fault as P0745 or P0746?

They are related but distinct. P0745 is a performance/stuck fault (solenoid not responding as commanded), P0746 is a stuck-off fault, and P0748 is specifically an electrical out-of-range fault. P0748 points directly to wiring or solenoid coil integrity rather than hydraulic performance.

Can I drive with P0748?

Limited driving in fail-safe mode is possible, but harsh shifts put stress on clutch packs and the drivetrain. Transmission overheating is a risk on longer trips. Prompt diagnosis is recommended to avoid accelerating internal wear.

Disabling P0748 in software

RaceTune can permanently disable P0748 — 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.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

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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