P0340 on Chevrolet: How to Diagnose & Fix
Camshaft Position Sensor Circuit Malfunction
1 Chevrolet model · 2 documented issues · 2 critical · $800-$2,000 repair
P0340 on Chevrolet by model: symptoms, diagnosis and fix
The LT1 (and 1996 LT4) uses a front-of-engine 'Opti-Spark' optical distributor mounted low behind the water pump, driven off the camshaft. It is highly vulnerable to moisture, heat, and ozone. The 1992-1993 units were completely unvented and are notorious for internal condensation and corrosion of the optical sensor disc. The leading real-world cause of failure is a leaking water pump directly above it dripping coolant onto/into the unit, but ordinary humidity and age also kill them. It is one of the single most defining reliability weak points of the 1992-1996 C4.
Common Symptoms
- Intermittent misfire
- Rough running / stumbling
- Stalling
- No-start (especially after rain or high humidity)
- Misfire that worsens when engine/weather is damp
- Backfiring
How to Fix
Replace the Opti-Spark distributor (later vented-style unit is the upgrade for 92-93 cars; a vacuum-vented design arrived on 1995-1996 units). Because the water pump sits directly above it and is the most common contaminant source, the accepted practice is to replace the water pump at the same time ('while you're in there'), since the front cover/serpentine and much labor overlaps. Many owners also drill/tap the water pump weep hole and route a hose away from the distributor.
Sources for this issue (1)
The 1992-1996 LT1 uses the Opti-Spark optical distributor mounted low on the front of the engine, directly behind the water pump. Undersized factory vent/drain holes trap condensation, and any coolant seepage from the water pump weep hole or oil from the front crank seal corrodes the optical sensor and internal contacts. When the high-resolution signal degrades, the engine misfires, backfires, and can stall without warning and refuse to restart, often stranding the owner. The 1995-1996 vented design lasts longer but still fails with age.
Common Symptoms
- Misfire or skip that worsens at higher RPM
- Backfiring through the intake or exhaust
- Stumbling or stalling in damp weather or after washing the engine
- Extended cranking or no-start
- Engine suddenly dies while driving and won't restart
- Rough idle
How to Fix
Replace the distributor with a vented (1995-96 style) or upgraded aftermarket Opti-Spark, and replace the water pump at the same time since pump leaks are a primary killer of the new unit. Labor is significant (roughly 4-7 hours) because the water pump, balancer, and accessories must come off; some owners convert to aftermarket coil-pack ignition.
Sources for this issue (1)
P0340 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0340 mean on a Chevrolet?
P0340 stands for "Camshaft Position Sensor Circuit Malfunction." This code means the engine computer lost or received an erratic signal from the camshaft position sensor. That sensor tells the computer the exact position and speed of the camshaft, which it uses together with the crankshaft sensor to time fuel injection and spark precisely. When the camshaft signal is missing, intermittent, or out of range, the computer sets P0340. Symptoms often include hard starting, stalling, rough running, or a no-start because the engine can't time itself correctly. On Chevrolet it is documented across 1 model: Corvette.
What are the most common causes of P0340?
The most common causes of P0340 are: Failed camshaft position sensor, Corroded or loose sensor connector, Damaged or shorted sensor wiring, Bad reluctor/tone ring on the camshaft, Loose timing chain/belt or jumped timing, Metal debris or oil contamination on the sensor tip, Poor sensor power or ground supply, Faulty PCM/ECM (rare). The specific cause varies by vehicle.
How much does it cost to fix P0340 on a Chevrolet?
Published repair estimates on Chevrolet range from $800 to $2,000 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0340 on a different make?
View P0340 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.