Comprehensive diagnostic guide for P0347 Camshaft Position Sensor A Circuit Low Input -- Bank 1

• The guide synthesizes general OBD-II code structure and diagnostic approach from Wikipedia's OBD-II sections (Diagnostic Trouble Codes, Powertrain Codes, Emissions Testing) to ground the discussion in terminology and standard flow for P-codes and powertrain diagnostics.
  • OBD-II: Diagnostic Trouble Codes - explains that modern vehicle systems use ECU-monitored parameters and generate trouble codes when issues are detected.
  • OBD-II: Powertrain Codes - places P codes in the powertrain category, guiding expectations about symptoms and diagnostic flow.
  • Emissions Testing - provides context for the role of diagnostics in emissions-related activity.
• Open-source code reference provided describes a low-input signal scenario for CKP/CMP sensor circuits (Bank A), which is related in concept to P0347's sensor-circuit fault family. This supports the sensor-circuit failure logic but is not a direct P0347 definition.

Overview

• Code: P0347
• Common interpretation: Camshaft Position Sensor A Circuit Low Input (Bank 1). In many makes/models, this is the signal input from the Camshaft Position Sensor A being read as abnormally low by the PCM. Exact wording can vary by manufacturer.
• System area: Powertrain, Camshaft Position Sensor circuit

Symptoms

• Most common: Malfunction Indicator Light (MIL) is on; diagnostic trouble code P0347 is stored.
• Vehicle performance symptoms (variable by engine design and the fault's severity):
  • Misfire symptoms (rough idle, intermittent misfires, reduced power)
  • Hesitation or lack of power during acceleration
  • Engine may run poorly at idle or stall in some cases
  • Tachometer behavior may be erratic or absent (depends on how the ECU interprets the sensor signal)
  • In some cases, no start or extended cranking if the PCM cannot establish timing
• Real-world user complaints aligned with sensor-circuit faults typically include "MIL on, rough idle, hesitation," and occasionally "no-start" scenarios in more severe timing-signal loss situations.
• If multiple related sensors or circuits are failing, you may see additional codes (e.g., P0335 or other CMP/CNK related codes) indicating broader crank/cam timing signal issues.

What This Code Means

• The PCM is not seeing a valid Camshaft Position Sensor A signal or is interpreting the signal as consistently too low in voltage or logic level.
• This disrupts accurate camshaft timing reference, which the ECU relies on for ignition and fuel timing.

Probable Causes

1) Faulty Camshaft Position Sensor (A) itself

• Most common cause in many engines; internal sensor failure or a degraded signal can read as a low input.
• Symptoms align with low/absent cam signal and a stored P0347.

2) Wiring harness/connectors to the Camshaft Position Sensor (A)

• Damaged, frayed, or pinched wires; poor or corroded connectors; water intrusion; harness rubbing on engine components.
• A damaged signal lead or a bad ground/return can produce a low-input appearance to the PCM.

3) Sensor power/ground issues (to CMP sensor A)

• 5V reference or ground instability supplied to the CMP sensor from the PCM can produce a low or distorted signal.
• Loose ground strap, corroded ground connection, or a failed reference circuit can manifest as a low input reading.

4) Electrical noise or shorted/weak signal due to adjacent circuits

• Intermittent short to ground or cross-talk on the signal line can create a misleading low input reading, especially at certain RPM ranges.

5) Timing-related mechanical issues (less common for mere "low input" signals, but possible in severe cases)

• If timing components (timing chain/belt, sprockets, variable cam timing mechanism) are physically out of specification, it can affect CMP signals; however, these typically produce broader timing faults and may be accompanied by other codes or symptoms.

6) PCM/ECU fault (rare)

• Infrequent, but possible: PCM misreads the sensor signal due to firmware/hardware fault; usually caught by cross-checks with other sensors or by confirming with another vehicle or known-good PCM.

Step-by-Step Diagnosis

1) Confirm and scope the issue

• Use an OBD-II scanner to confirm P0347 is active and note any secondary codes.
• Review freeze-frame data for engine RPM, vehicle speed, engine load, and PCM sensor readings at the time the code was stored.
• Confirm whether the code reappears after clearing and re-cranking.

2) Visual inspection and basic wiring checks

• Inspect CMP Sensor A and its wiring harness for obvious damage, melted insulation, exposed conductors, or signs of heat/abrasion where it passes near moving parts.
• Inspect connector for corrosion, bent pins, or poor latch engagement. Disconnect and reconnect firmly to reseat.
• Inspect grounds: ensure a solid engine block ground and any CMP sensor ground path are clean, tight, and free of corrosion.
• Check for oil leaks or coolant contact that could contaminate the sensor or harness.

3) Electrical power/ground verification (CMP sensor circuit)

• With key ON (engine OFF), backprobe the CMP sensor harness:
  • Verify that the 5V reference (if the CMP uses a 5V reference) is present at the sensor reference pin.
  • Verify that the ground is solid at the sensor ground pin.
• Using a DVOM (digital volt-ohm meter) or oscilloscope (preferred for waveform), verify:
  • Stable 5V reference on the reference circuit (if applicable).
  • A clean signal output from the CMP A circuit during crank (look for a clean, periodic waveform corresponding to cam lobes; a persistently low voltage or a flat line indicates a fault).

4) Sensor signal testing (live data)

• With the engine cranking, read the CMP A signal with live data:
  • If the sensor is functioning, you should see a periodic signal correlated with engine RPM (frequency increases with RPM).
  • If the signal is stuck at a low level or absent, suspect CMP sensor, wiring, or PCM input circuit.
• If the vehicle uses a secondary CMP or Bank B sensors, compare Bank A vs Bank B signals (if available) to determine if the issue is sensor-specific or a common PCM problem.

5) Physical sensor inspection or replacement trial

• If the CMP A sensor looks suspicious (age, heat exposure, physical damage), replace with a known-good unit and re-test.
• When replacing, ensure correct alignment/tolarances and proper torque on mounting bolts if applicable.

6) Harness/wiring repair

• Repair or replace damaged wiring or connectors as needed.
• If a harness fault is suspected but not easily located, perform a continuity check from the CMP A sensor to the PCM connector and inspect for shorts to power or ground.

7) Confirm timing system integrity (as a supplementary check)

• If CMP signal is now good but timing appears suspect (e.g., misfire persists, or timing-related symptoms remain), verify timing chain/belt, sprockets, tensioners, and alignments per factory procedure.
• Note: Timing mechanical issues are less likely to cause a standalone "low input" reading unless the sensor is misreading due to mechanical interference or misalignment. Consider this step if symptoms persist despite a good CMP signal.

8) PCM/controller considerations

• If the CMP circuit and sensor are confirmed good, and the wiring is clean, but the code still returns, consider a PCM fault or firmware issue as a last resort.
• Reflash or reprogramming is rare in a diagnostic sense but can be necessary if software faults exist. Use manufacturer guidance for this step.

9) Clear codes and perform road test

• After repairs, clear codes and perform a road test to confirm no reoccurrence and to ensure the vehicle runs normally under load, idle, and at various RPM ranges.

What data to collect during testing (recommended)

• Live sensor data for CMP A (voltage or digital signal level) across RPM range.
• 5V reference voltage presence and stability (reference circuit integrity).
• Ground continuity and resistance from sensor ground to PCM ground.
• Any ignition or engine misfire data that correlates with the CMP signal status.
• Scan tool freeze-frame data before and after testing.

Repair Actions

• If CMP A sensor is found defective: replace sensor and re-test.
• If wiring/connectors are damaged: repair or replace the affected harness segment and reseat connectors.
• If 5V reference or ground is intermittent: repair ground path or reference supply wiring, ensure solid ground points.
• If sensor signal is clean after repair but code returns: consider PCM fault and discuss with the manufacturer service procedure for the specific model.
• After any repair: clear codes, run a road test, and re-scan to verify the code does not reappear.

Safety Considerations

• Disconnect battery before disassembly when working near electrical connectors or sensor housings.
• Be mindful of hot engine components and stored energy in ignition systems during testing.
• Use proper PPE and avoid shorting circuits with test equipment.

Summary of key points

• P0347 is a Camshaft Position Sensor A Circuit Low Input issue (Bank 1) within the OBD-II P-code family (powertrain). The PCM expects a valid camshaft position signal from Sensor A; a low input disrupts timing and can trigger MIL and misfire-related symptoms.

• The most common causes are a faulty CMP sensor, wiring/connectors problems, or ground/power supply issues to the sensor. Mechanical timing issues are possible but typically accompanied by broader timing symptoms or other codes.

• A structured diagnostic approach - verify code, inspect wiring/connectors, test power/ground/reference, monitor live CMP signal, replace the CMP sensor or repair wiring as indicated, and re-test - yields a safe, comprehensive path to repair.

• Documentation and interpretation should reference the general OBD-II coding framework (Diagnostic Trouble Codes; Powertrain Codes) as described .

• Wikipedia - OBD-II: Diagnostic Trouble Codes (overview of how codes are structured and used by ECUs) and Powertrain Codes (classification of codes including P-codes) to ground the diagnostic framework. See sections on Diagnostic Trouble Codes and Powertrain Codes for context.

• Open-source code reference (CKP/CMP sensor context): An entry describing low input signals for CKP/CMP sensor Bank A, which aligns with the sensor-circuit fault family described in this guide. This supports the relevance of sensor-circuit integrity in P0347-type issues.

• Practical caution: If manufacturers' exact wording and wiring schemes differ (5V reference vs. other configurations), adapt the test steps to your model's service information. The general approach remains the same: verify sensor, harness, ground, and signal integrity, then confirm with live data and targeted tests.

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.

---