Comprehensive Diagnostic Guide for OBD-II Code P0746

Topic: Pressure Control Solenoid A - Performance or Sticking (P0746)

What This Code Means

• What the code means: P0746 is a Powertrain/OBD-II code that indicates an issue with the Pressure Control Solenoid A . This aligns with the general idea that the solenoid or its control circuit is not operating within expected parameters.
• Context: DTCs are generated by the vehicle's on-board diagnostics as part of the powertrain control system. Modern systems continuously monitor parameters and will set a code when a sensor, actuator, or circuit deviates from expected ranges. This is described in the Diagnostic Trouble Codes and Powertrain Codes sections of the OBD-II material.
  • sources: OBD-II - Diagnostic Trouble Codes; OBD-II - Powertrain Codes

Symptoms

• Transmission symptoms most commonly associated with P0746:
  • Harsh or delayed or erratic downshifts and/or upshifts
  • Transmission slipping or reluctance to engage gear
  • Intermittent or persistent harsh engagement when selecting drive or reverse
  • Transmission "limp mode" or limited gear selection due to PCM protection
  • Erratic or poor transmission performance under load (e.g., accelerating onto highway ramps)
• Note: Symptoms can be similar to other transmission hydraulic or electrical faults, so a focused diagnostic approach is essential.

Probable Causes

Because do not include NHTSA complaint statistics for this code, probabilities below are based on typical ASE-field experience and the general understanding that P0746 relates to the solenoid circuit and its control. These should be treated as rough probabilities and adjusted for vehicle make/model and observed data.

• Solenoid A (pressure control solenoid) failure or intermittent operation - ~40-60%
  • The solenoid itself can fail open/short, stick, or fail to modulate hydraulic pressure properly, leading to improper transmission pressure and shift issues.
• Wiring harness or connector issues to solenoid A (including corrosion, damaged insulation, or loose connections) - ~20-30%
  • Poor electrical connection can prevent the PCM from properly energizing the solenoid.
• Transmission control module (TCM/PCM) command or calibration issues - ~5-15%
  • Software/firmware problems or a faulty driver in the PCM/TCM can miscommand the solenoid.
• Transmission fluid level/condition issues affecting hydraulic pressure (low fluid, dirty/contaminated fluid, failed filter) - ~5-15%
  • Inadequate or degraded hydraulic fluid can affect valve body operation and solenoid response.
• Valve body or internal transmission hydraulic/mechanical faults (non-solenoid related pressure leakage, stuck valves, worn valve body passages) - ~5-10%
  • Internal wear or contamination can mimic or amplify solenoid-related symptoms.
• Other related circuit faults (e.g., other solenoids on the same circuit, or multiple DTCs present) - variable
  • Additional DTCs can point to more systemic hydraulic/electrical issues.

What to check before you start (safety and prep)

• Safety: Park on a flat surface, engage parking brake, vehicle in Park (or Neutral for engine tests with caution as applicable), and block wheels as needed. When working with the transmission circuit, avoid starting or moving the vehicle with exposed wiring or solenoids.
• Tools you'll likely need:
  • OBD-II scan tool with live data capability
  • Digital multimeter and back-probing access to solenoid circuit
  • Vehicle service manual or manufacturer wiring diagrams for solenoid A circuit
  • Fluid drain/fill equipment if fluid service is indicated
• Gather the vehicle details: make, model, year, transmission type, and any related stored codes or freeze-frame data.

Diagnostic Approach

1) Confirm and contextualize the code

• Use an OBD-II scan tool to confirm P0746 is stored and check for any related codes (e.g., other transmission codes such as P0740, P0741, P0750, etc.). Note freeze-frame data and live data at the time of a fault.
• Check for manufacturer-specific P0746 definitions in the vehicle's service information, as the exact solenoid naming and circuit details can vary by model.

2) Gather symptoms and drive data

• Document customer-reported symptoms (shifts, engagement, limp mode behavior) and attempt to reproduce the condition on a controlled drive if safe.
• While driving, monitor live data for the transmission: trans fluid temperature, solenoid A circuit voltage, solenoid duty cycles (or commanded vs. actual) and any abrupt changes in pressure-related signals.

3) Electrical health of solenoid A circuit

• Visual inspection: Examine the wiring harness and connectors for damage, corrosion, or pin issues at the solenoid A connector.
• Power and ground: With ignition on (engine off for resistance tests if needed), back-probe the solenoid A power supply and ground to verify stable voltage and a solid ground path. Symptome of a flaky supply or ground manifest as intermittent voltages or inconsistent solenoid operation.
• Resistance measurement: Measure the solenoid A coil resistance with the ignition OFF. Compare against the manufacturer's specified resistance range. A resistance far outside spec indicates a faulty coil.
• Command verification: While the vehicle is operated, verify that the PCM/TCM is actually commanding the solenoid (via the scan tool if supported by the vehicle). Look for signs that the commanded duty cycle or voltage is not reaching the solenoid.

4) Fluid and hydraulic considerations

• Transmission fluid level and condition: Check the transmission fluid level hot (per service manual) and assess the fluid's color and odor. A low or degraded fluid can affect hydraulic pressure and solenoid performance.
• Fluid service: If fluid is very old, burnt, or contaminated, plan a proper fluid change and replace the filter if applicable. This step can resolve some hydraulic-related symptoms without replacing components.
• External leaks: Inspect for hydraulic leaks in the trans assembly and lines that might influence system pressure.

5) Vehicle operation and data correlation

• If possible, perform a controlled test with the vehicle in gear (drag or load conditions) while monitoring the solenoid A circuit and the transmission pressure signals. Look for a discrepancy between commanded solenoid operation and actual response (pressure/solenoid control).
• If live data shows the solenoid is commanded but no corresponding hydraulic response is observed, suspect solenoid or valve body/hydraulic circuit components.

6) Mechanical and internal transmission considerations

• If electrical checks and fluid/service do not resolve the fault, consider internal valve body wear, solenoid valve wear, or other hydraulic circuit problems within the transmission.
• In some cases, a valve body cleaning/rebuild or replacement of the pressure control solenoid assembly is required.

7) Software and calibration checks

• Check for TCM/ECU software updates or recalls that address transmission control strategies for your vehicle. A software issue can masquerade as a faulty solenoid or circuit.
• If software-related, follow the manufacturer's instructions for reflashing or updating the TCM/PCM.

8) Decision branch: repair vs. replacement

• If electrical issues are confirmed (bad solenoid, wiring, or connector) and no internal hydraulic fault is found, perform the appropriate solenoid assembly repair/replacement and restore proper circuit integrity.
• If hydraulic/valve body faults are evident or fluid quality is poor and consistent with the symptoms, address hydraulic components (solenoid assembly, valve body, filter, and fluid) as required.
• If multiple critical hydraulic components are failing or the transmission has significant internal wear, a transmission replacement or rebuild may be necessary.

Diagnostic Tests

• Confirm P0746 and related codes; document freeze-frame data.
• Inspect and test solenoid A circuit: power/ground integrity, connector condition, and coil resistance.
• Verify PCM/TCM commanded signal vs actual solenoid operation with live data.
• Check transmission fluid level and condition; perform service if warranted.
• Assess for valve body issues or other hydraulic faults (valve body inspection, possible cleaning/rebuild).
• Review software/firmware for the TCM/PCM and apply updates if available.
• If faults remain after electrical and hydraulic checks, prepare for transmission expert diagnosis (possible valve body service, solenoid assembly replacement, or transmission replacement).

Repair approaches (typical)

• Electrical
  • Replace or repair solenoid A assembly.
  • Repair/replace wiring harness or connectors; clean or pin-dress connections.
  • Reprogram or update TCM/PCM software if required by the manufacturer.
• Hydraulic
  • Replace pressure control solenoid A and related seals/gaskets in the valve body as needed.
  • Clean or rebuild valve body; replace seals and o-rings.
  • Flush transmission fluid, replace filter (if applicable), and refill to specification.
• Mechanical
  • If internal wear or damage is evident from subsequent diagnostics, consider valve body overhaul or transmission rebuild/replacement.
• After repair
  • Clear DTCs, perform a relearn or drive cycle as required by the vehicle to ensure proper engagement and shift behavior.
  • Re-check for DTCs after a test drive; verify that the fault does not reoccur.

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II

Content synthesized from these sources to provide accurate, real-world diagnostic guidance.

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