Comprehensive diagnostic guide for OBD-II code P0928

Topic focus: Open circuit in the shift lock solenoid circuit (shift lock interlock)

Important Notes

• Based on the Open Source OBD-II definitions provided, P0928 is described as an "open circuit of the shift lock solenoid" . This aligns with a shift lock interlock solenoid circuit fault. The exact OEM interpretation of P0928 can vary by manufacturer, so verify against the factory service information for the specific vehicle if possible.
• In general OBD-II practice, DTCs are produced by the powertrain control system when a parameter is out of acceptable range or a circuit fault is detected. The shift lock solenoid circuit is part of the transmission/shift interlock hardware controlled by the vehicle's powertrain/body electronics. If the open circuit condition is detected, the PCM/TCM may set P0928 and illuminate the MIL.

Symptoms

• Vehicle cannot be moved out of Park (or cannot shift out of Park to Neutral or Drive). The shift interlock may prevent movement entirely.
• Brake pedal interlock or shift interlock warning lights are active or flicker; brake pedal depressions do not reliably enable shifting.
• Intermittent no-start or failure to engage transmission into gear when commanded.
• DTC P0928 appears with other related transmission/lock solenoid codes or sensor codes during a scan.
• In rare cases, symptoms appear during cold starts or after a sport/drive mode selection, with the interlock solenoid receiving erratic signals.

How this code generally fits into the system

• The shift lock solenoid is part of the transmission shift interlock system. It is designed to lock the gear selector unless the brake is applied and the proper interlock conditions are met. An open circuit in the solenoid circuit can prevent the solenoid from energizing, allowing or preventing movement as designed depending on the fault location and vehicle logic.
• The condition is typically detected as an open circuit (infinite resistance) or loss of supply/return path to the solenoid, or a fault in the controlling module that documents an open circuit condition to the PCM/TCM.

Probable Causes

Note: do not include NHTSA complaint data for P0928. Where possible, percentages are framed from general field experience and typical diagnostic patterns, with an explicit note when data is not available .

• Most common: Faulty shift lock solenoid or its wiring/connector (open circuit in the solenoid loop, damaged harness, loose or corroded connectors). This typically accounts for the majority of P0928-type symptoms.
  • Estimated probability in practice: 40-60%
• Wiring harness or connector damage in the solenoid circuit (incomplete circuit, pin corrosion, pin push-out, insulation damage, harness chafing).
  • Estimated probability: 15-30%
• Faulty or intermittent power supply to the solenoid (fuse, relay, or BCM/TCM output control) causing an open circuit condition or lack of drive to the solenoid.
  • Estimated probability: 5-15%
• Control module issues (PCM/TCM/BCM) commanding the solenoid incorrectly or going into fault state (may present as open circuit in the solenoid circuit in some vehicle implementations).
  • Estimated probability: 5-10%
• Mechanical issue with the shift interlock mechanism or lock cylinder that prevents normal operation even if the solenoid circuit is intact (less common but possible).
  • Estimated probability: 0-5%
• Other related sensor/grounding issues that cause the control logic to misinterpret the circuit status (e.g., ground integrity, sensor inputs affecting interlock enable).
  • Estimated probability: 0-5%

Safety Considerations

• Work on the interlock system requires the vehicle to be stationary and properly secured. Do not attempt to force the shift out of Park if the interlock is malfunctioning; confirm the problem safely.
• Disconnect battery only if necessary and follow proper anti-spark procedures to avoid short circuits or airbag system concerns. If you must probe electrical circuits, use proper PPE and insulated tools.
• Ensure the vehicle is on a flat, level surface with parking brake applied when performing tests that could inadvertently move the vehicle.

Tools and information you'll want

• OBD-II scan tool capable of reading DTCs and, if possible, commanding solenoids or reading live data PIDs related to the interlock system.
• Multimeter (digital preferably) for resistance/continuity testing and voltage checks.
• Vehicle service information for the specific make/model (to locate the shift lock solenoid, related fuses/relays, connector pinouts, and expected resistance values). Wikipedia notes the general concept of diagnostic systems and powertrain codes in OBD-II contexts (for high-level understanding) but you'll need the factory manual for exact specs.
• Wiring diagram for the shift interlock solenoid circuit (to inspect harness routing, connectors, grounds, and power feeds).
• If applicable, a test light or a traceable supply to energize the solenoid for functional testing under controlled conditions.

Diagnostic procedure (step-by-step)

Preparation

• Confirm DTC P0928 is present and note any freeze-frame data, MIL status, and any related DTCs (especially other transmission or interlock-related codes).
• Check the vehicle's battery condition and charging system; a weak battery can cause intermittent solenoid operation. Refer to service data for acceptable voltage ranges.

1) Visual inspection and basic electrical checks

• Visual: Inspect the shift interlock solenoid and its harness for obvious damage, corrosion, pin misalignment, melted insulation, and chafed wires along the harness route.
• Connectors: Check the solenoid connector for corrosion, bent pins, and secure engagement. Reseat connectors if needed.
• Fuses/relays: Verify the fuse(s) and any relay controlling the shift lock solenoid circuit. Replace any blown fuses and test relays for proper operation.
• Grounds: Inspect the ground path for the solenoid circuit. A bad ground can mimic an open circuit.

2) Power and signal verification

• With ignition on (engine off if required by the vehicle software), probe the solenoid circuit at the connector:
  • Measure supply voltage to the solenoid when the brake pedal is applied (if the system energizes the solenoid in brake/interlock condition). Compare to expected values in service data.
  • Check for continuity between the solenoid coil and its ground reference.
• If no voltage is present, backtrace to the source (fuse/relay, wiring harness, or control module output). If voltage is present but no current flows, test for a short to ground or open coil.
• If the vehicle uses a controlled solenoid (solenoid is driven by the BCM/TCM), confirm that the control module is issuing the command (if accessible via the scan tool and data PIDs). Note: Some vehicles may not expose direct solenoid drive data in standard OBD-II readers.

3) Functional testing of the solenoid circuit

• If safe and the vehicle's service procedure allows, energize the shift lock solenoid with a known-good 12V supply (through appropriate wiring and current-limiting). Observe whether the solenoid actuates and whether the shift lock mechanism can be released or engaged as intended.
• A controlled test with the scan tool (if the tool supports solenoid control) can confirm whether the PCM/TCM can command the solenoid and whether the solenoid responds consistently.
• If energizing the solenoid externally fails to actuate, the solenoid is likely defective (replace). If energizing the solenoid works but the vehicle still reports an open circuit, suspect wiring or control logic.

4) Correlation with other components and signals

• Check related interlock components and signals that enable the solenoid:
  • Brake switch signal (some systems energize the solenoid only when the brake is applied).
  • Park/neutral safety switch or gear selector module (depending on design) for proper state.
  • Transmission control module communications that could affect interlock operation.
• Review any related DTCs (for example, transmission-related codes that could point to a broader interlock or valve body issue).

5) Wiring harness and connector testing

• Perform resistance checks along the solenoid circuit to locate opens or high-resistance sections (wiring harness, splices, connectors).
• Inspect for insulation damage and moisture intrusion at connectors.
• If a fault is found, repair or replace the damaged section and re-test the circuit.

6) Repeatability and cross-checks

• Clear the DTCs after repairs and drive the vehicle through normal operating cycles (as per OEM procedures) to verify the fault does not reoccur.
• If DTC P0928 returns, re-check the solenoid, wiring, and control module for intermittent faults, and re-verify all connections and grounds.

Repair Options

• Most likely fix: Replace or repair the shift lock solenoid and/or its wiring harness/connector if an open circuit is confirmed.
• If wiring or harness damage is found: Repair or replace affected wiring and connectors. Re-test to ensure integrity.
• If the fault is traced to a fuse/relay issue: Replace defective fuse/relay and confirm continuity and power supply to the solenoid.
• If control module fault is suspected: Consult OEM service information for module reprogramming, updated software, or module replacement. This is generally less common but possible.
• Mechanical issues: If the solenoid and wiring are sound but the lock mechanism remains jammed or physically seized, inspect the shift interlock assembly and mechanism for mechanical binding or wear.

Documentation

• Document all tests performed, values measured, and conclusions drawn.
• Record any component replacements, wiring repairs, and software/firmware updates, along with part numbers and service dates.
• Re-scan for codes after repairs and verify that P0928 is cleared and that the vehicle shifts normally.

Relation to the broader OBD-II context

• OBD-II codes provide a standardized framework (DTCs) for diagnosing issues across vehicle systems. P0928 is a transmission/shift interlock-related code in the P0xxx powertrain family. The general approach-verify symptoms, test circuits, inspect wiring and connectors, and verify control-module operation-follows the standard diagnostic methodology described in the OBD-II overviews (Diagnostic Trouble Codes; Powertrain Codes) on Wikipedia. This guide follows that framework while focusing on the shift lock solenoid circuit as described by the open-source code definition .

Documentation

• A shift lock circuit fault (P0928) often points to the interlock solenoid, its wiring, or its control circuit. The most common fix is replacing or repairing the solenoid or damaged wiring. If the fault is from a control module or a fuse/relay, the repair path will depend on the specific vehicle and its service data.

• After any repair, a road test or drive cycle is usually performed to confirm that the interlock operates correctly and that the vehicle can shift normally.

• Open Source OBD2 CODE DEFINITIONS: The provided entry lists P0928 with the description (Open circuit of the shift lock solenoid). This provides the functional meaning for the code in this context and guides the fault-domain focus toward the shift lock solenoid circuit.

• Note on data availability: do not include explicit NHTSA complaint data for P0928. Therefore, probabilities for causes are based on generalized field experience and standard diagnostic logic rather than a quantified dataset from NHTSA in the supplied material.

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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