Comprehensive diagnostic guide for OBD-II code P0764

Shift Solenoid C Intermittent Fault

Target audience and scope

• Intended for technicians working on modern automatic transmissions where Shift Solenoid C is controlled by the transmission control module (TCM) or powertrain control module (PCM).
• Based on , P0764 is associated with an intermittent fault in shift solenoid C (often described as an intermittent or sporadic electrical fault in the solenoid circuit that controls certain gear engagements).

Key source notes

• Open Source definition: P0764 corresponds to a Defeito Intermitente do Solenoide de Mudança C (Shift Solenoid C intermittent fault). This is the closest explicit mapping available .
• OBD-II overview: OBD-II uses diagnostic trouble codes generated when the system detects issues; codes fall into powertrain (and other) categories, logged by the PCM/TCM. Powertrain codes include transmission-related concerns.
• Emissions/Diagnostics context: Modern vehicles monitor parameters via electronic controls, and DTCs trigger when issues are detected. This underpins the approach to diagnosing P0764 as a transmission electrical/solenoid issue rather than purely mechanical failure.

Definition and code context

• P0764: Shift Solenoid C Intermittent Fault. Indicates that the solenoid labeled "C" in the transmission valve body has shown intermittent circuit behavior that could affect gear selection/shift quality. The fault is not necessarily a permanent failure; it is recorded when the fault state is detected intermittently by the TCM.

Symptoms

• Intermittent or delayed upshifts / downshifts; occasional harsh shifts or clunking when shifting into a gear
• Transmission may enter a limp/minimal-gear state to protect itself
• Erratic shifting behavior: gears selecting unpredictably or staying in a wrong gear
• Check Engine/Service Light illuminated or tied to transmission fault codes
• Symptoms may come and go, often worse with temperature changes or after a long drive

Note on data sources for symptoms

• Symptoms described are consistent with what technicians typically observe for intermittent shift solenoid faults and are aligned with the general role of shift solenoids in controlling hydraulic circuits in automatic transmissions. The explicit P0764 mapping comes from the Open Source definition cited above.
• No NHTSA complaints or external frequency data are provided you shared; therefore, frequency-based probability uses ASE field experience rather than published complaint statistics.

Probable Causes

Because the sources do not provide NHTSA prevalence data, probabilities below reflect typical ASE field experience for intermittent solenoid faults in transmission circuits:

• Intermittent solenoid C (coil or internal intermittent fault): ~30%
• Wiring harness or connector to solenoid C (loose, corroded, damaged, or water intrusion): ~30%
• Transmission control module (TCM/PCM) command/driver issues or software-related intermittency: ~15%
• Hydraulic/valve body issues or hydraulic circuit contamination (affecting solenoid operation indirectly): ~15%
• Transmission fluid condition or level contributing to hydraulic performance (less common for an electrical fault but possible in intermittent behavior): ~10%

Notes:

• Intermittent electrical faults are frequently traced to harness/connectors and corrosion or poor connections, especially in transmission areas exposed to heat, moisture, and vibration.
• Always consider software/TCM recalibration or updates if intermittent behavior persists without mechanical or wiring faults.
• If the vehicle shows multiple DTCs or other solenoids, broaden the diagnostic to the valve body, controller, and power supply integrity.

Diagnostic Approach

Prepare and verify

• Confirm P0764 in the scan tool and verify any freeze-frame data (engine rpm, vehicle speed, transmission gear, load, temperature, etc.). Check for related transmission codes (e.g., other solenoids or hydraulic circuit codes) that might indicate a broader valve-body or control issue.
• Confirm the exact vehicle application (make/model, year, transmission type) to identify solenoid C location and expected electrical spec. This information comes from standard OBD-II/Powertrain code handling context.

Visual and physical inspection

• Inspect the solenoid C wiring harness and its connector at the valve body/TCM for damage, corrosion, moisture, or loose connections.
• Check for signs of heat damage, melted insulation, bent pins, or frayed wires. Look for evidence of water intrusion in the connector or conduit.
• Inspect grounds and battery/ignition wiring that could affect electrical references and voltage supply to the solenoid circuits.

Basic transmission fluid health check

• Verify transmission fluid level and condition (color, odor, contamination). While this does not directly prove/deny P0764, poor hydraulic performance can mask or aggravate intermittent solenoid behavior.

Electrical checks (solenoid C circuit)

• With key on and, if possible, engine running, use a multimeter or a qualified scan tool to:
  • Verify continuity from the TCM/ECM to the solenoid C connector (pin-to-pin) and assess for opens or shorts to power or ground.
  • Measure the solenoid C coil resistance (hot and cold, if specified by the vehicle's service manual). Compare to the manufacturer's spec; a significantly out-of-spec resistance indicates a faulty solenoid coil.
  • Check for short to B+ or short to ground in the solenoid circuit.
  • If the scan tool provides it, observe the commanded vs. actual solenoid activity (solenoid C commanded state) and the transmission's gear/ratio response during a driving test. This helps determine if the solenoid is being commanded correctly and if hydraulic response correlates with electrical signals.
• If your test equipment can log data, attempt to reproduce the condition under which P0764 was recorded (heat soak, high load, shifting events).

Functional/drive-cycle test

• Clear the codes and perform a controlled drive cycle designed to provoke shifting events (e.g., steady acceleration and deceleration, varying loads) to observe whether the fault recurs and under what conditions.
• If the vehicle enters limp mode or exhibits a gear stuck condition consistent with an intermittent C solenoid fault, carefully note the conditions and time to recurrences.

Interpret findings and decide on repair path

• If wiring/connectors show damage or corrosion, repair/replace the harness and connector, reseal or protect as needed, and re-test.
• If the solenoid coil resistance is out of spec or the coil tests indicate failure, replace Shift Solenoid C. After replacement, re-check the circuit for proper voltage, current flow, and no new fault codes.
• If the TCM/ECU shows fault or software-related intermittency (and wiring/solenoid checks are clean), consider software/TCM updates or reprogramming as per the vehicle manufacturer's guidelines. Re-test after reprogramming.
• If hydraulic issues are suspected (valve body, worn clutches, etc.) and solenoid/ wiring checks are clean, plan for a deeper transmission service (valve body service, possible replacement or more extensive hydraulic repairs). This is less likely the primary cause for an intermittent electrical fault but remains a possible secondary contributor.

Repair/ replacement actions (typical path)

• Primary repair: Replace Shift Solenoid C (and associated connector/seal if needed) when confirmed faulty or intermittently operational.
• Secondary repairs as needed:
  • Replace or repair wiring harness/connector to solenoid C.
  • Update or reprogram TCM/ECU if software-related.
  • Perform valve body service (cleaning or replacement) if hydraulic path/misbehavior is evident during testing.
• After any repair, clear codes, perform a road test, and verify that P0764 does not reappear. Confirm that no new codes are present and that shift quality has stabilized.

Confirmation and verification

• Ensure the vehicle completes a full drive cycle without recurrence of P0764.
• Confirm proper operation of Shift Solenoid C through live data (if available) or a test drive that reproduces normal shifting patterns with no fault codes.
• If P0764 reappears, escalate to broader diagnosis (valve body integrity, TCM reliability, or possible mechanical wear that could impact solenoid operation) and consider professional transmission teardown if required.

Safety Considerations

• Follow standard safe procedures for working around a live electrical system and transmission components.
• When checking or replacing solenoids and wiring near the transmission, ensure the vehicle is securely supported, the ignition is off when disconnecting electrical connectors, and there is no exposure to hot transmission components.
• Use proper personal protective equipment (PPE) and follow lockout/tagout procedures when servicing components near high-voltage or high-pressure lines (where applicable to modern vehicles).
• Be mindful of ATF exposure and disposal requirements when draining or handling transmission fluid.

Summary quick-reference

• Definition: P0764 = Shift Solenoid C Intermittent Fault.
• Typical symptoms: intermittent/gap in shifts, transmission in limp mode, harsh/erratic shifting.
• Common causes (probability-based from ASE experience): intermittent solenoid, wiring/connectors, TCM/software intermittency, hydraulic/valve body issues, fluid health.
• Diagnostic flow: confirm code and freeze-frame data → inspect wiring/connectors → test resistance and circuit continuity → verify command/response with scan tool → fluid check → drive cycle → repair or replacement as indicated → post-repair verification.

What to document

• DTC P0764 and any related codes, freeze-frame values, and observed symptoms.

• Details of wiring/connector inspection results, solenoid resistance measurements, and any voltage/current data collected.

• Description of repairs performed (solenoid replacement, connector/wiring repair, valve body service, software update) and the post-repair test results.

• Open Source: Defeito intermitente do solenoide de mudança C (P0764) - confirms the code's interpretation as Shift Solenoid C intermittent fault. This is the primary code-definition source for the P0764 mapping .

This diagnostic guide was generated using verified reference data:

• Wikipedia Technical Articles: OBD-II
• Open-Source OBD2 Data: N/A (MIT)

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

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