P0325 on GMC: How to Diagnose & Fix
Knock Sensor 1 Circuit Malfunction (Bank 1)
1 GMC model · 1 documented issue · $400-$900 repair
P0325 on GMC by model: symptoms, diagnosis and fix
The 4.8L, 5.3L, and 6.0L Vortec engines used in early GMT800 Sierra trucks place the knock sensors in wells beneath the intake manifold, where water can collect and corrode the sensors or harness. Owners frequently report recurring check-engine lights, timing retard, and reduced power, especially after washing the engine bay or driving in wet conditions. GM issued service information addressing knock sensor corrosion and revised sealing practices.
Common Symptoms
- check engine light
- reduced power
- poor acceleration
- intermittent spark retard
- codes return after rain or washing
- rough running under load
How to Fix
Diagnosis involves scanning for knock sensor circuit codes, checking freeze-frame data, and inspecting the sensor wells and sub-harness under the intake for moisture or corrosion. Proper repair is replacement of both knock sensors and the harness, cleaning the valley area, and resealing the intake and sensor openings with the updated grommets/sealant procedure to prevent repeat failures.
Sources for this issue (1)
P0325 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 P0325 mean on a GMC?
P0325 stands for "Knock Sensor 1 Circuit Malfunction (Bank 1)." This code indicates a fault in the knock sensor 1 circuit on Bank 1. The knock sensor listens for the vibrations of detonation (pinging/spark knock) and lets the computer retard ignition timing to protect the engine. When the sensor's signal is missing, out of range, or the circuit is open/shorted, P0325 sets. With knock detection compromised, the computer may run more conservative timing, causing reduced power and slightly lower fuel economy, and the engine is less protected against damaging knock. On GMC it is documented across 1 model: Sierra 1500.
What are the most common causes of P0325?
The most common causes of P0325 are: Failed knock sensor, Corroded or loose knock sensor connector, Damaged, open, or shorted sensor wiring, Improperly torqued or loosely mounted sensor, Moisture or corrosion in the connector, Wiring harness chafing near the engine, Faulty PCM/ECM (rare). The specific cause varies by vehicle.
How much does it cost to fix P0325 on a GMC?
Published repair estimates on GMC range from $400 to $900 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 P0325 on a different make?
View P0325 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.