P0323 -- Ignition/Distributor Engine Speed Input Circuit Intermittent

P0323 - Ignition/Distributor Engine Speed Input Circuit Intermittent

What This Code Means

• P0323 indicates an intermittent fault in the engine speed input circuit to the Powertrain Control Module (PCM). The input is the signal that tells the PCM the engine speed (often from the ignition/distributor pickup or the crank/cam reference sensor, depending on engine architecture). The circuit is not continuously failing, but the PCM sees an unstable or intermittent signal when the engine is running, which sets the MIL and stores the code.

Symptom description (typical user reports you may see)

• MIL (Check Engine Light) illuminated or pending.
• Tachometer behaves erratically or goes to zero in instances; engine speed input seems unstable to the PCM.
• Intermittent rough idle, stalling, or hard starting/cranks without starting.
• Occasional misfire-like symptoms during acceleration, especially when engine speed transitions quickly.
• In some cases, vehicle runs normally for a period, then intermittently exhibits speed-signal related symptoms; the issue often appears under certain vibrations, temperature changes, or engine loading.

Probable Causes

• Wiring and connectors in the ignition/distributor speed input circuit (loose/dirty/abused terminals, pin oxidation, cracked wiring insulation). 40-60%
• Faulty ignition pickup in the distributor (or crank/cam sensor in distributorless configurations) causing an intermittent signal to the PCM. 15-30%
• Wiring harness damage or intermittent ground/return path affecting the speed-input circuit. 5-15%
• PCM/input circuit fault (internal PCM issue or software anomaly) producing intermittent signal interpretation. 5-15%
• Other related sensor or control issues that disrupt timing reference (e.g., related timing components) but not the primary speed input. 5-10%

Note: The above probabilities reflect typical ASE field experience and are not drawn from a single NHTSA data source . these can be refined.

Pre-Diagnostic Checks

• Confirm the DTC with a scan tool and review freeze-frame data. Verify whether P0323 is current or intermittent and check for any related codes (e.g., P0320-P0325 family codes that involve ignition or speed-input references).
• Visually inspect the ignition speed input circuit:
  • Connectors at the ignition pickup/distributor sensor or crank/cam reference sensor (depending on engine type). Look for corrosion, bent pins, moisture intrusion, loose fit, or torn wiring.
  • Wiring harness for abrasion, heat damage, or pinch points along the route to the PCM.
  • Ground connections and engine/PCM grounds that service the signal circuit.
• Use a live data stream or oscilloscope whenever possible to observe the engine-speed signal:
  • With engine cranking and running, confirm a stable, clean signal is present from the ignition pickup/CKP/CFP (as applicable).
  • Look for intermittent dropouts, noise, spikes, or loss of signal that correlates with symptoms.
• Inspect ignition/distributor hardware (if applicable):
  • If your vehicle uses a distributor, inspect the ignition pickup coil and reluctor/wheel, and the distributor itself for wear.
  • For distributorless systems, inspect crankshaft and/or camshaft position sensors and associated adapters.
• Electrical supply and grounding checks:
  • Verify sensor supply voltage and ground integrity; check for battery voltage drops or grounding faults that occur during engine movement (vibrations, steering lock, etc.).
• Mechanical correlation:
  • Consider timing reference misalignment or timing belt/chain issues if the engine speed signal shows unusual waveform shapes or timing discrepancies.

Step-by-Step Diagnosis

1) Establish baseline

• Retrieve P0323 with a quality scan tool; note engine RPM waveform shape if the tool provides it. Confirm whether the fault is intermittent or persistent through cycles or road tests.
• Review any related codes and engine operating conditions when the fault occurs (temperature, load, RPM range).

2) Visual and mechanical inspection

• Inspect all connectors in the ignition speed input circuit at the sensor/coil and PCM harness side; reseat and clean as needed.
• Inspect the wiring harness for damage or chafing; repair or replace damaged sections.
• Check for corrosion in connector terminals; apply dielectric grease if appropriate after cleaning.
• Inspect grounds to the PCM and engine block; ensure clean, tight connections.

3) Electrical tests (circuit-level)

• With key on, verify sensor power supply and ground at the input circuit connector using a DVOM. Confirm voltages are within spec per service information for your vehicle.
• With the engine running or cranking, watch the signal input to the PCM on the scan tool or with an oscilloscope. Look for intermittent signal loss or waveform irregularities.
• Wiggle-test the wiring harness and connectors to reproduce the intermittent condition; note any changes in signal or code status.
• If applicable, perform a resistance check on the sensor (ignition pickup, crank/cam sensor) per service documentation; compare to specification.

4) Sensor integrity assessment

• If the signal is consistently present when tested and the wiring checks out, suspect the sensor (ignition pickup/CKP/CKP-related sensor) as the fault and plan for replacement.
• If the signal fails intermittently during tests, suspect sensor or connector/wiring in the immediate circuit path, including the connector pins and the harness.

5) PCM consideration

• If wiring and sensor tests pass but the issue persists, consider PCM input circuit fault (internal PCM fault or software) as a possibility. This is less common but should be considered after all wiring/sensor tests.

6) Road test and recheck

• After repairing or replacing components, clear codes, re-test drive under typical operating conditions, and confirm the P0323 does not reoccur.
• Recheck for any new codes that may appear and verify related sensor data remains within spec.

Recommended repairs based on findings

• If wiring/connectors are the root cause:
  • Repair or replace damaged wiring, clean or replace corroded pins, reseat connectors, and apply appropriate protective measures (e.g., heat-shrink, loom, dielectric grease where appropriate).
• If a sensor is failing:
  • Replace the ignition pickup coil/distributor sensor or crank/cam reference sensor, depending on the vehicle's ignition architecture.
• If grounding or power supply is suspect:
  • Repair/replace any compromised power/ground paths to the sensor or PCM; ensure solid ground connections and clean power supply.
• If PCM input circuit fault is suspected:
  • Consider PCM replacement or reprogramming/service procedure as directed by the vehicle's service information, after excluding harness/sensor faults.
• If related components are present (e.g., timing components), address those as necessary to restore proper timing reference.

Safety Considerations

• High-voltage ignition systems can be dangerous; follow standard safety procedures when inspecting ignition components.
• Depower the electrical system before disconnecting connectors in the ignition/distributor circuit, and wear protective gear.
• When using an oscilloscope or scope-capable multimeter, observe all safety precautions to avoid electric shock or short circuits.

Related codes and context

• OBD-II DTCs are organized into Powertrain Codes and other groups; P0323 is categorized within powertrain concerns that affect emissions and engine control.
• The exact wording for P0323 in an open-source/ GitHub-like definition is "Sinal de rotação do motor CKT intermitente - Ignição/distr.", aligning with the description of an intermittent engine speed input circuit for ignition/distributor.

Tips and traps

• Don't assume a failed sensor is always the cause; intermittent faults often come from wiring/connectors or grounding issues.
• Always verify with live data; a false impression of a good signal can happen if the fault is intermittent or temperature dependent.
• If multiple codes appear, prioritize the speed-input circuit (P0323 or near codes) as the possible primary fault, but confirm no secondary issues exist.

Documentation

• Vehicle make/model/year, engine type (distributor vs. distributorless), and the exact sensor(s) involved.
• Location of all affected wiring and connectors found, any corrosion or damage, and the repair performed.
• Test results (voltage, resistance, scope waveforms) before and after repair.
• Road-test results and whether codes reappear.

Reference sources (for further reading and verification)

• Wikipedia - OBD-II: Diagnostic Trouble Codes: Provides general context on DTCs, their role in modern automotive diagnostics and the powertrain codes grouping.
• Open Source OBD2 Code Definitions: "Sinal de rotação do motor CKT intermitente - Ignição/distr." indicating the code description in the context of engine speed input circuit intermittency for ignition/distributor.

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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