P0340 on 2002-2004 Holden Commodore 3.8L V6: Cam Sensor Causes and Fixes

What's Unique About the 2002-2004 Holden Commodore

While many vehicles get a P0340 code from a simple sensor failure, the Holden Ecotec 3.8L V6 has a unique and very common point of failure. The camshaft position sensor reads a small magnet pressed into the camshaft sprocket. Over time, the plastic cage holding this magnet can become brittle and break, allowing the magnet to fall out or shatter. This leads to a P0340 code even if the sensor and wiring are perfectly fine. A user on the Just Commodores forum confirmed this was their issue after replacing the sensor didn't work, stating, "It appears I may have found the culprit. A missing magnet on the camshaft gear." Diagnosing this specific issue first can save you from replacing a perfectly good sensor.

Symptoms You May Notice

• Engine is difficult to start or cranks but won't start.
• Extremely rough idle, sometimes stalling at stops.
• Significant loss of engine power and poor acceleration.
• Check Engine Light is on.
• Increased fuel consumption.
• Engine hesitates or stutters during operation.

Most Likely Causes

1. Missing or Damaged Camshaft Sprocket Magnet 🔴 High Probability → Shop Engine Camshaft The plastic retainer for the magnet on the cam sprocket becomes brittle with age and heat cycles, causing the magnet to break or fall out. This is a well-documented issue in Holden forums, with one user noting, "I found that the cam sensor pickup magnet, which is located in the camshaft sprocket, had fallen out of its hole in the sprocket."
   How to confirm: Remove the single 10mm bolt holding the camshaft position sensor and pull the sensor out of the timing cover. Use a small inspection mirror and a light to look at the camshaft sprocket through the hole. You should see a small, metallic magnet embedded in the sprocket. If it's gone or you see broken plastic pieces, you've found the problem. A user on Just Commodores posted a photo of the empty hole on their sprocket, confirming the missing magnet.
   Typical fix: The timing cover must be removed to access the camshaft sprocket. A new magnet must be pressed into the sprocket. Some owners on US-based forums for the similar Buick 3800 engine suggest modifying the new magnet by grinding off the 'brim' and securing it with epoxy or high-strength adhesive to prevent it from falling out again. This is a labor-intensive job.
   Est. part cost: $20-$80 for the magnet.
2. Faulty Camshaft Position Sensor 🟡 Medium Probability → Shop Engine Camshaft Position Sensor Like any electronic component exposed to high engine temperatures, the sensor itself can fail internally over time. It's a common replacement part, but often misdiagnosed when the magnet is the real issue.
   How to confirm: If you have confirmed the cam magnet is present and the wiring is good, the sensor is the next most likely culprit. It can be tested with a multimeter by checking for a changing voltage signal while the engine is cranked, but replacement is often the most straightforward confirmation for a DIYer.
   Typical fix: Replace the camshaft position sensor. It is held in by a single 10mm bolt and is accessible from the front of the engine.
   Est. part cost: $70-$180
3. Damaged Wiring or Connector ⚪ Low Probability The wiring harness in the engine bay is exposed to heat and oil, which can make the wires brittle or the connector faulty over time. Wires can break inside the insulation, making visual diagnosis difficult.
   How to confirm: Visually inspect the wiring leading to the camshaft position sensor for any signs of cracking, fraying, or melting. Check the connector for corrosion, oil contamination, or backed-out pins. A multimeter can be used to check for continuity and proper voltage at the connector.
   Typical fix: Repair the damaged section of wiring or replace the connector pigtail. A forum user suggested carefully closing up the female terminals in the connector to ensure a tight fit.
   Est. part cost: $15-$50

Rare But Worth Checking

• Faulty Powertrain Control Module (PCM): → Shop Engine Control Module (ECM) This is very rare. The PCM is the last thing to suspect after all other possibilities (magnet, sensor, wiring) have been definitively ruled out.
• Stretched Timing Chain: → Shop Engine Timing Chain While more common on the later VE Commodore's Alloytec V6, a significantly stretched timing chain on an Ecotec can cause the cam/crank correlation to be out of sync, potentially triggering cam-related codes. This would typically be accompanied by rattling noises from the front of the engine.

Diagnosis Steps

1. Retrieve the trouble code with an OBD-II scanner to confirm P0340 is present.
2. Inspect the wiring harness and electrical connector at the camshaft position sensor. Look for any visible damage, corrosion, or oil contamination. Check for backed-out terminals.
3. Remove the camshaft position sensor (held by one 10mm bolt) from the front timing cover.
4. Using an inspection mirror and flashlight, carefully look through the sensor mounting hole at the camshaft sprocket. Verify that the small, round magnet is present and intact. This is the most critical step for this vehicle.
5. If the magnet is missing or broken, the timing cover must be removed for repair. This is the most likely cause.
6. If the magnet is present and the wiring looks good, the sensor itself is the next likely failure point. Test the sensor with a multimeter or replace it with a quality part.
7. If a new sensor does not resolve the issue, perform a continuity and voltage test on the wiring between the sensor connector and the PCM.
8. After any repair, clear the trouble codes with the scanner and perform a test drive to ensure the fix was successful.

Parts You'll Likely Need

• Camshaft Position Sensor (OEM #10456162) — This is the second most common failure point after the cam magnet and is a straightforward replacement if the magnet is confirmed to be intact.
  Trusted brands: Delphi, ACDelco, NTK
  OEM price range: $120-$180
  Aftermarket price range: $70-$110
• Camshaft Sprocket Magnet (OEM #25530386) — This is the most probable cause of P0340 on this specific engine due to a known design weakness where the retaining plastic fails.
  Trusted brands: Genuine Holden/GM, ZZPerformance
  OEM price range: $20-$80
  Aftermarket price range: $15-$30

Platform-Specific Known Issues

• The plastic housing for the magnet on the camshaft timing gear is known to become brittle and fail, causing the magnet to fall out or shatter. This is the most common cause of P0340 on the Ecotec V6.

Mechanic-Grade Diagnostic Values

• Cam Sensor Connector - Power Supply Voltage — expected: 12V (Battery Voltage). Failure: Significantly less than 12V indicates a wiring or DFI module supply issue.
• Cam Sensor Connector - Signal Wire Voltage (Key On, Engine Off) — expected: ~5V DC. Failure: 0V or significantly less than 5V suggests a faulty sensor, a short in the wiring, or a bad PCM driver.
• Cam Sensor Connector - Ground Pin to Chassis Ground — expected: Near 0 Ohms (continuity). Failure: High resistance or an open circuit (OL) indicates a bad ground wire or connection, which will cause the sensor to malfunction.
• Cam Sensor Signal (Active Test) — expected: Voltage should drop from ~5V to 0V when a piece of metal is passed in front of the sensor tip.. Failure: If the voltage does not change, the sensor is faulty.

Wiring & Ground Locations

• Cam Sensor Connector (3-Pin) — Front of the engine, inserted into the timing cover, near the water pump.. This is the primary connection point for all sensor tests. It typically has a 12V power wire, a ground wire, and a 5V signal wire.
• GP5 - Engine Block Ground — Front Right-Hand Side of the engine block.. This is a primary engine ground point. A loose or corroded connection here can cause various sensor issues, including for the cam and crank sensors which rely on a stable ground reference.
• DFI Module Ground — The DFI (Distributorless Ignition System) module itself is grounded to the engine. The cam sensor receives its power via the DFI module.. A poor ground at the DFI module can cause erratic voltage supply to the cam sensor, triggering a P0340 even if the sensor and its direct wiring are good.
• PCM Connector X1-B6 — At the Powertrain Control Module (PCM), typically located in the engine bay near the firewall or passenger side strut tower.. This is the specific pin where the camshaft position sensor signal arrives at the PCM. A diagnostic chart mentions checking for backed-out terminals at this location.

Real Owner Repair Stories

• Just Commodores forum user (Holden Commodore (VS, similar Ecotec V6)) — Cranks but no start, no spark, no injector pulse.
  ❌ Tried (didn't work) Replacing the DFI module, Replacing the Crank Angle Sensor, Replacing the Cam Angle Sensor
  ✅ What actually fixed it A broken wire for the cam angle sensor was found inside the loom near the air conditioning compressor. The insulation was intact, but the copper wire inside was broken, requiring a continuity test to find.

OEM Part Supersession History

• 10456162 → 10456148 (often cited as an alternative or replacement) — Standard part evolution and manufacturer changes.
  Heads up: While both part numbers are associated with the Ecotec V6 cam sensor, it is crucial to match the sensor to the specific model year. Delphi is a primary OEM supplier for this part.

Diagnostic Flowchart

Other Known Issues on This Vehicle

Issues unrelated to this code that are worth knowing about as an owner of this generation:

• Leaking Intake Manifold Gaskets 🔴 High → Shop Engine Intake Manifold — Very common failure as the vehicle ages, typically over 150,000 km. The original plastic/rubber gaskets degrade, causing coolant and/or oil leaks.
• Failing Harmonic Balancer 🔴 High — Common after 100,000-150,000 km. The rubber bonding layer between the inner hub and outer ring deteriorates.
• Leaking Oil Pressure Switch/Sensor 🟠 Medium — Common failure item. The sensor itself can leak oil through its body and into the electrical connector.
• Power Window Regulator/Motor Failure 🟡 Low — Extremely common across all doors. The plastic clips and cables in the regulator assembly are prone to breaking.

Used vs. New Parts: Buying Guide for This Vehicle

When a used part is the smart pick: A used OEM (e.g., Delphi, ACDelco) camshaft position sensor from a low-mileage wreck can be a viable option and may be more reliable than a cheap, new, no-name aftermarket sensor. However, given the relatively low cost of a new quality aftermarket sensor, it's often not worth the risk.

Donor-vehicle mileage cap: roughly under 80000 miles for the part to have meaningful remaining life.

What to inspect on the donor part:

• Check for physical damage to the sensor body and connector.
• Avoid sensors from engines that show signs of heavy oil leaks or overheating.
• If possible, ask for the mileage of the donor vehicle.

OEM-only on this vehicle (don't cheap out):

• Camshaft Sprocket Magnet - This part fails due to age and heat-related brittleness. A used magnet is just as old as the one that failed and is not a wise purchase. Always buy this new.

Aftermarket brands forum-validated for this vehicle:

• Delphi (OEM supplier)
• NTK
• ACDelco

Brands owners have reported issues with on this vehicle:

• Unbranded, 'white box' sensors from online marketplaces are frequently cited on forums as having high failure rates or being dead-on-arrival.

Real Owner Stories

Aggregated from forums and TSBs cited above. Mileages and costs reflect what owners reported in those sources.

Related OBD-II Codes

• CODE 41 — This is the equivalent manufacturer-specific diagnostic code used in related GM 3800 Series II platforms for camshaft sensor circuit failure, often triggered by the same missing magnet issue.

Frequently Asked Questions