Comprehensive diagnostic guide for OBD-II P2079

Overview

• P2079 is a powertrain-related diagnostic trouble code referenced in open-source definitions as (intermittent position sensor or switch circuit). This interpretation comes from an open-source MIT-repo listing for P2079; OEM definitions can vary. Use OEM service information for your specific vehicle when available.
  • Note: Wikipedia's OBD-II sections explain how DTCs are generated and classified as Powertrain Codes, but they do not provide the exact meaning for every P-code. This means the P2079 interpretation may differ between sources and vehicle makes.

What P2079 commonly indicates

• Based on the open-source listing and typical DTC behavior, P2079 generally points to an intermittent issue in a position sensor/switch circuit. This could involve:
  • Crankshaft or camshaft position sensor circuit intermittently losing or corrupting the signal
  • The associated wiring, harness, or connector intermittently failing or becoming high-resistance
  • A weak or failing position sensor itself
• Because the code is described as intermittent, the fault may not be present at all times, making live-data capture and wiggle testing essential.

Symptoms

• MIL (Check Engine Light) illuminated, often with P2079 stored and possibly pending.
• Intermittent engine stalling, misfires, or bucking at various RPMs.
• Intermittent no-start or extended cranks that eventually start.
• Rough idle that comes and goes, sometimes correlated with engine temperature or load.
• Irregular engine timing-related symptoms (especially if a crank/cam position sensor is involved).
• Inconsistent or abnormal engine running during acceleration vs. deceleration.

Probable Causes

Note: The following probabilities are informed by field experience (ASE-level diagnostic practice) when specific NHTSA complaint data for P2079 is .

• Intermittent/cracked or high-resistance signal in the position sensor circuit (sensor, harness, or connector): 40-60%
• Faulty position sensor itself (crank or cam position sensor) failing intermittently: 20-40%
• Intermittent bad/loose connector or wiring harness damage (pin corrosion, loose ground, damaged insulation): 5-15%
• ECU/PCM input issue (faulty input pin, software/firmware quirk, or power/ground instability feeding the sensor circuit): 5-15%
• Grounds or supply voltage instability affecting the sensor circuit (battery/charging issues or poor grounding): 5-10%
• Other mechanical timing issues or sensor-position misalignment (less common; may indicate broader timing system concerns): 0-5%

What to do before you start heavy testing (safety and prep)

• Confirm P2079 is present with a reliable scan tool and note any related codes. Check freeze-frame data and any pending codes.
• Inspect for any vehicle-specific service bulletins (TSBs) that address intermittent position sensor issues.
• Ensure the battery is healthy and the charging system is within spec; dV/dt issues can cause intermittent sensor readings.
• Gather service information for the exact sensor(s) involved in your vehicle (crankshaft camshaft position sensors, or any other position switch) so you know what to test.

Step-by-Step Diagnosis

Step 1 - Gather data and reproduce

• Use a capable OBD-II scan tool to confirm P2079 is stored and to view live data PIDs related to position sensors (if available for the vehicle).
• Note engine RPM behavior, engine load, and any correlations with vehicle speed, temperature, or humidity.
• If possible, review any related codes (e.g., P0335-P0336 for crank position, P1336 for cam timing, etc.) to narrow down the sensor involved.

Step 2 - Visual inspection

• Inspect all wiring and connectors to the position sensor(s) (crank/cam or switch circuits). Look for:
  • Loose, corroded, bent, or damaged pins
  • Damaged insulation, crushed harness, or signs of water ingress
  • Deteriorated heat shielding or routing that could cause vibration or chafing
• Check ground and power supply wires for the sensor circuit; ensure solid ground references.
• Look for aftermarket repairs or damaged wiring looms that might introduce intermittent faults.

Step 3 - Identify the exact sensor(s) involved

• Determine whether the code maps to crankshaft position, camshaft position, or another position/switch sensor for the engine or transmission. The exact sensor depends on vehicle design; service information is key.
• If the vehicle uses dual position sensors (e.g., crank + cam), verify which channel is implicated by any related data or by pattern of related codes.

Step 4 - Electrical tests on the sensor circuit

• Power supply and reference:
  • With the ignition ON (engine off) verify the sensor power supply voltage (e.g., 5V reference) and ground with a digital multimeter (DVOM).
  • Check for stable reference voltage and a solid ground path; look for high resistance that could cause intermittent readings.
• Signal integrity:
  • Back-probe the sensor signal wire and measure the signal waveform with an oscilloscope (preferred) or a high-quality DVOM with a fast sampling rate.
  • Look for clean, periodic signal pulses with stable amplitude. Intermittent issues may show missing pulses, jitter, or erratic waveform when the engine runs.
  • If the sensor has a secondary output (e.g., differential or hall effect signal), verify both channels compare appropriately.
• Sensor heater (if applicable):
  • Some position sensors include a heater circuit. If a heater is present, test its circuit for proper operation; heater failures can cause intermittent sensor behavior in some conditions.

Step 5 - Mechanical/operational correlation testing

• Perform a "wiggle test" on the wiring harness and connectors while monitoring the sensor signal on a scope or scan tool. Look for momentary dropouts or noise that coincides with movement.
• If the engine uses a crank or cam position sensor with reluctor wheel or toothed pulley:
  • Check for physical interference, belt/ pulley misalignment, or timing mechanical issues that could influence signal consistency.
  • Ensure timing components (timing belt/chain, cam/crank gears) are within specification; a timing issue can manifest as intermittent position-signal problems.

Step 6 - Cross-check with related sensors and systems

• Compare the position sensor signal to other related sensor data (e.g., compare crank vs. cam sensor pulses if both monitored by the PCM). Large phase shifts or misalignment between them can help pinpoint the problem area.
• Check for other codes that might indicate a broader PCM or sensor family issue (e.g., generic sensor errors, misfire, or ignition-related codes).

Step 7 - Advanced diagnostics (if available)

• Use a scope to view the waveform pattern under different engine conditions (cold start, warm idle, high rpm, and load). Intermittent issues often appear only under specific conditions.
• If the vehicle supports enhanced data logging, capture multiple short sessions to look for a pattern (e.g., sensor signal disappears during high load, after heat soak, or during rapid throttle inputs).
• If you have access to a known-good sensor or harness in the same vehicle platform, perform a swaps-and-tests approach to isolate the faulty component.

Step 8 - Decision and repair

• If the position sensor signal is intermittent or out of spec and the harness/connector checks are clean, replace the affected position sensor first (assuming crank/cam sensor is identified as the probable source).
• If the wiring harness or connector is intermittently failing (poor connection, corrosion, insulation damage), repair or replace the wiring and connectors, and re-check.
• If a PCM input is suspected (rare), consider PCM service alternatives per OEM guidelines; in many cases, a software update or reflash may be indicated, but confirm with the vehicle's service information.
• After any repair, clear codes and perform a road test to confirm the issue is resolved and no new codes appear.

Post-Repair Validation

• Clear P2079 and perform a road test under multiple conditions (cold start, warm idle, acceleration) to ensure no recurring symptoms.
• Re-scan after testing to confirm the code does not return and monitor live data to verify stable position-sensor signals.
• If the code returns intermittently, re-check the harness for hidden damage or consider alternate sensors in the same circuit.

Safety Considerations

• Work with the ignition off and battery disconnected when performing wiring/connector service to avoid short circuits.

• If using an oscilloscope, follow proper safety procedures when probing live circuits.

• If the vehicle is under warranty or you're working on a critical engine timing sensor, adhere to OEM service procedures and torque specs for any fasteners or connectors involved.

• OBD-II fundamentals and P-code contexts: Wikipedia - OBD-II - Diagnostic Trouble Codes; Wikipedia - OBD-II - Powertrain Codes. These sources explain the general framework for DTCs and powertrain codes, and the role of the ECU in fault detection.

• Open-source definition mapping for P2079: Pos Sensor / Switch Circ Interm. This listing provides the interpretation that P2079 corresponds to an intermittent position sensor or switch circuit. Note that OEM definitions can vary across manufacturers.

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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