Comprehensive diagnostic guide for OBD-II code P0390

Definition and scope (what the code means)

• P0390 is described in open-source code definitions as a malfunction of the crankshaft position sensor (CKP) circuit for Bank B (i.e., the CKP sensor on Bank 2). In simple terms, the PCM is seeing an abnormal or faulty signal from the CKP sensor that corresponds to Bank B. This is consistent with the generic role of CKP circuits in providing crank position timing data to the PCM.
  • Source notes: Open Source definition (Crankshaft Position Sensor circuit malfunction, Bank B) [OBD2 CODE DEFINITIONS].
  • Context: In the broader OBD-II framework, DTCs are generated by the powertrain control system when monitored parameters indicate faults. This is described in the general DTC and Powertrain code discussions.

Probable Causes

Note: do not include NHTSA complaint data. The following probability guidance reflects typical field experience for CKP/Bank B circuit issues. Percentages are best-effort estimates and can vary by model and maintenance history.

• CKP sensor (Bank B) failure or internal fault: ~40%
  • Symptoms would align with degraded or absent CKP signal (no timing reference to PCM).
• CKP sensor wiring harness damage or connector corrosion/damage in the Bank B circuit: ~30-35%
  • Common in harness routes near heat, flex zones, or where vibration occurs; may produce intermittent or degraded signal.
• Mechanical timing/reluctor issues associated with Bank B (e.g., damaged reluctor wheel or misalignment, timing-related hardware): ~10-15%
  • Depending on engine design, a mechanical fault can mimic CKP signal problems or create aberrant timing data.
• PCM/ECU input fault or internal fault: ~5%
  • Less common, but possible if the ECU has degraded ADC input, damaged CKP channel, or a correlating wiring fault.
• Short to ground/open in CKP circuit (water intrusion, corrosion, poor insulation) or other electrical contamination: ~5%
  • Can produce intermittent or erratic CKP readings.
• Notes: If multiple CKP-related codes or driveability issues exist, joint root causes (wiring, connector, or sensor location) should be investigated first.

Diagnostic Approach

1) Verify and document

• Retrieve all stored and pending codes with a capable scan tool. Note any related codes (e.g., P0335 Crankshaft Position Sensor A circuit, P0336 CKP range/performance, or P0339 CKP sensor A circuit intermittent, etc.).
• Review freeze-frame data for Bank B CKP activity (if available) to see what engine conditions were present when the code occurred (RPM, load, temperature, etc.).
  • Context: DTCs are documented and used by the PCM to monitor parameters; this is a standard part of OBD-II diagnostics.

2) Visual and basic electrical inspection

• Inspect Bank B CKP sensor and its wiring harness:
  • Look for damaged insulation, chafed wires, exposed conductors, loose or corroded connectors.
  • Check for signs of heat damage or water ingress in the CKP sensor connector and wiring harness routing.
• Inspect electrical grounds and battery/alternator condition, as poor grounding can affect sensor signals.
• If accessible, gently wiggle the Bank B CKP connector and harness while monitoring the CKP signal (with a scope or oscilloscope) to check for intermittent contact issues.

3) Basic circuit checks (with appropriate test equipment)

• Power and ground: verify CKP sensor supply voltage (typically 5V reference from the ECU and a stable ground). Look for dropouts or excessive resistance.
• Signal circuit test: measure the CKP output signal with an oscilloscope or a diagnostic scope, looking for a clean, periodic waveform corresponding to crankshaft speed. A missing or irregular waveform supports a CKP circuit fault rather than a sporadic mechanical fault.
• Resistance checks (as applicable per manufacturer): check sensor coil resistance and/or circuit resistance as specified in the service information for Bank B CKP sensor. Note: exact resistance values vary by sensor type and engine design; consult the vehicle's service data if available.
• Compare Bank B vs Bank A (if the engine has a Bank A CKP as reference): anomalous readings on Bank B compared to Bank A can indicate a Bank-specific issue or a common wiring problem.

4) Cross-check with related sensors and data

• Check related timing references that may influence CKP interpretation (e.g., CMP/Camshaft Position sensors, if vehicle uses a cam/crank synchrony system). In some engines, cam/crank coordination is monitored collectively; a fault in one can affect overall timing data.
• Look for any misfire, fuel trim, or idle quality codes that could signal timing data issues rather than a pure wiring fault, and correlate with CKP data.
• If you have access to a live data stream, compare CKP signal characteristics with engine RPM and other timing-related parameters to assess consistency.

5) Mechanical inspection considerations

• If electrical checks fail to identify a clear fault, consider mechanical issues in Bank B timing components (reluctor ring condition, mounting accuracy, debris, or timing chain/blex belt integrity) as a possible source of a degraded CKP signal.
• Ensure the engine is at proper top-dead-center timing reference if attempting to inspect timing hardware.

6) Reproduce and isolate

• After performing repairs or replacements (sensor or wiring), clear the codes and perform a test drive to confirm the issue is resolved.
• Monitor for reoccurrence of P0390 and verify that related CKP-related codes do not reappear.

Recommended tests to perform (practical guidance)

• Oscilloscope waveform check of CKP output (Bank B): look for stable, periodic waveform corresponding to RPM; no signal or irregular waveform supports a CKP circuit fault.
• Reference voltage and ground test for Bank B CKP circuit using a DVOM or test scope:
  • 5V reference should be stable; low or erratic reference can cause incorrect CKP readings.
  • Ground integrity should be solid with minimal voltage drop.
• Continuity and insulation test of CKP wiring harness and connector between CKP sensor and PCM input. Look for high resistance, shorts, or opens.
• If available, compare Bank B to Bank A CKP signal behavior to identify asymmetry indicating a bank-specific fault.
• After replacement or repair, perform a drive cycle to ensure the code clears and does not return.

Repair and Verification

• If the CKP sensor is determined to be faulty (Bank B), replace the CKP sensor and re-torque/fit per manufacturer specs; ensure the sensor seating depth and alignment comply with service data.
• If wiring/connectors show damage, repair or replace harness segments and repair/replace the connector (including seals and weatherproofing as needed).
• If mechanical timing components are suspected, follow the vehicle's service procedure for inspecting and re-installing timing components (timing belt/chain, tensioners, sprockets, and related hardware). Only perform timing work if you have the correct tooling and understand the engine's timing reference procedure.
• After any repair, clear DTCs, reset adaptive memory as required by the vehicle, and perform a controlled drive cycle to confirm the P0390 code does not return.
  • Emissions testing implications: As P0390 relates to engine timing data, unresolved CKP circuit faults can affect emissions performance and readiness.

Documentation

• Explain that P0390 indicates a problem with the CKP sensor circuit on Bank B (Bank 2) and that the engine control module uses this signal to manage timing. Warranty/repair options may include sensor replacement, wiring harness repair, or timing component inspection depending on findings.
• Outline the diagnostic steps performed and the rationale for the recommended repair. Provide an estimated repair timeline and cost range (sensor, wiring, or timing work) based on the vehicle's make/model and the actual fault found.
• Emphasize the importance of rechecking after repair to ensure the issue is resolved and to prevent roadside or no-start issues in the future.

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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