# P0325: Knock Sensor 1 Circuit (Bank 1 or Single Sensor) **Verdict:** Drive to a shop this week Engine sensors - Generic OBD-II code, applies to all gasoline cars and light trucks sold in the US since 1996. - **Typical cost:** $150-$1,200 - **Urgency:** This week - **Most likely:** Failed knock sensor or damaged wiring - **DIY?:** Shop job on most engines ## Quick answer P0325 means the engine computer sees a problem in the electrical circuit of knock sensor 1, the sensor that listens for engine knock (pinging). The cause is usually a failed sensor or a damaged wire or connector, not actual knocking. Without a working knock sensor, the computer pulls back ignition timing to protect the engine, which can cost some power and fuel economy. ## What does P0325 mean? A knock sensor is a small piezoelectric sensor bolted to the engine block or cylinder head. It turns vibration into a small voltage, and the engine computer listens for the sharp frequency of knock, or detonation: fuel igniting uncontrolled, which can damage pistons. When it hears knock, the computer retards ignition timing until it stops. That lets the engine run close to the edge for the best power and fuel economy. P0325 is a circuit code. The computer sets it when the sensor signal or voltage is outside its expected range, from an open or short, or in some designs from no signal at all. "Sensor 1" means the first or only knock sensor, and "bank 1" means the side of a V engine that holds cylinder 1. Many makers need the fault on two drive cycles before the light comes on. Meanwhile, the computer runs a safer, retarded timing map. ## What are the symptoms of P0325? - Check engine light on - Slightly less power, especially when accelerating hard or climbing hills - Lower fuel economy than usual - Pinging or rattling under load on some engines ## What causes P0325? Ranked from most to least likely. Check them in this order: the cheap, common causes first. 1. **Failed knock sensor** (most common). The sensor is a small piezoelectric part that turns engine vibration into a signal, and its crystal and internal connections can fail after years of heat cycles. Failure often appears on higher-mileage engines with no other symptoms. A shop measures resistance where the maker publishes a value, or watches its signal on a scope while tapping near it. 2. **Damaged wiring or corroded connector** (common). The knock sensor wire is thin and often shielded, and it runs near hot engine parts where insulation can crack or melt. Rodents chew it, especially on cars parked outdoors for long periods. Corroded connector pins, or coolant leaking onto a sensor in the engine valley, can also break the signal. A shop inspects the harness end to end. 3. **Sensor bolted at the wrong torque** (less common). Knock sensors work by feeling vibration through the metal they bolt to, so mounting torque matters. A sensor left loose or overtightened after engine, intake or timing work may give a weak or distorted signal. Some makers also forbid washers or thread sealant under the sensor. This cause is most likely when the code appeared soon after other repairs. 4. **Engine computer (PCM) fault** (rare). Inside the engine computer, a dedicated circuit processes the knock signal, and it can fail from water intrusion, voltage spikes or internal faults. This is rare, so a shop rules out the sensor, wiring and connector first. If a known-good sensor and repaired wiring still set P0325, the computer is checked for software updates or replaced and programmed. ## How do you diagnose P0325? 1. Read the code and check whether a related knock sensor code (such as P0330 for bank 2) is also stored. 2. Inspect the knock sensor connector and the wiring you can reach for damage, corrosion, or rodent chewing. 3. Measure the sensor's resistance and check the circuit for opens and shorts using the specifications for your engine. 4. Check that the sensor is torqued to specification if it was recently disturbed. ## How do you fix P0325, and what does it cost? | Fix | Typical cost | What it involves | | --- | --- | --- | | Repair knock sensor wiring or connector | $150-$400 | Many engines have a separate knock sensor wiring harness that can be replaced on its own. | | Replace knock sensor (easy-access location) | $200-$450 | Applies when the sensor is on the side of the block and reachable. | | Replace knock sensor under the intake manifold | $500-$1,200 | Many V6 and V8 engines hide the sensors in the valley under the intake, which means hours of labor. | ## Is it safe to drive with P0325? > **Drive to a shop this week.** It is generally safe to drive for a while, since the computer retards timing to protect the engine. Avoid low-octane fuel and heavy towing, and stop if you hear loud knocking. ## Will P0325 fail an emissions test? A car with P0325 and the check engine light on fails an OBD-based emissions inspection, even though the knock sensor has little effect on tailpipe readings. The comprehensive component monitor watches this circuit continuously. After the repair, clear the code and drive normally until the noncontinuous readiness monitors show complete before going back for the test. ## After the repair: clearing P0325 Clear the code and road-test under moderate load, such as accelerating up a hill, when the computer listens hardest for knock. Where the scan tool shows it, check that knock retard reads near zero in normal driving. If the light stays off through several days of mixed driving and power and mileage return to normal, the circuit is fixed. ## How to prevent P0325 - Use the fuel octane your owner's manual specifies, especially when towing or in hot weather. - Discourage rodents in parked cars, since they chew engine wiring, including knock sensor harnesses. - Fix coolant and oil leaks that can soak a knock sensor connector in the engine valley. - Ask for the knock sensor to be torqued to specification after any engine or intake work. ## Codes often seen with P0325 - [P0300](/codes/p0300): Random/Multiple Cylinder Misfire Detected - [P0335](/codes/p0335): Crankshaft Position Sensor "A" Circuit - [P0340](/codes/p0340): Camshaft Position Sensor "A" Circuit (Bank 1 or Single Sensor) ## Frequently asked questions ### Can I drive with a P0325 code? Yes, in most cases you can drive normally while you schedule a repair. The engine computer switches to safer, more conservative timing, so you may notice slightly less power and worse mileage. Use the recommended fuel grade and avoid heavy towing until the sensor circuit is fixed. ### Does P0325 mean my engine is knocking? Usually not, because P0325 is a circuit problem with the sensor or its wiring, not a report of real knock. If you hear loud pinging or rattling under load, that is a separate concern. Use the correct fuel, and have the shop check for carbon buildup or overheating if the noise continues. ### Why is knock sensor replacement so expensive on some cars? The sensor itself is cheap, but on many V-type engines it sits in the valley under the intake manifold. Removing the intake takes several hours of labor plus new gaskets, which is where most of the bill comes from. On engines with the sensor on the side of the block, the job is much cheaper. ### Will using premium gas fix P0325? No, fuel grade does not fix a sensor circuit fault. If your car calls for premium, keep using it, because without a working knock sensor the engine has less protection from knock. The sensor or its wiring still needs repair before the code will clear and stay off. ### How much does it cost to fix P0325? Most P0325 repairs cost $150 to $450 when the wiring or an easy-to-reach sensor is the cause. On V6 and V8 engines with the sensor under the intake manifold, the bill often runs $500 to $1,200 because of labor. The sensor itself is usually inexpensive, so access drives the price. ### Where is the knock sensor? On most inline engines it is bolted to the side of the engine block, often below the intake manifold. On many V6 and V8 engines it sits in the valley between the cylinder banks, under the intake. Some engines mount it on the cylinder head, so check service information for yours. ### What is the difference between P0325 and P0330? P0325 is the circuit code for knock sensor 1, on bank 1 or the only sensor, while P0330 covers knock sensor 2 on bank 2. Both codes together often point to a shared harness or connector, which some V engines route under the intake manifold, rather than two failed sensors. ### Can a bad knock sensor cause engine damage? Rarely by itself, because the computer switches to conservative timing when the sensor circuit fails. The risk rises if you use lower-octane fuel than recommended, tow heavy loads or drive in extreme heat, since the computer can no longer detect real knock. Use the correct fuel until it is repaired. ### Can I replace a knock sensor myself? On engines where the sensor is on the side of the block and reachable, a careful DIYer can do it with a torque wrench. Sensors under the intake on V engines require removing the intake manifold, new gaskets and careful reassembly, which is usually a shop job. Always torque the sensor to specification. ### Will P0325 pass inspection? No, an active P0325 with the check engine light on fails an OBD-based emissions inspection. The repair rarely changes tailpipe emissions, but the light must be off and the readiness monitors complete. After the repair, clear the code and drive several days of normal trips before retesting. ## Sources - [SAE J2012: Diagnostic Trouble Code Definitions](https://www.sae.org/standards/content/j2012_201812/) ## Other engine sensors codes - [P0316 Engine Misfire Detected on Startup (First 1000 Revolutions)](https://diagxcar.com/codes/p0316) - [P0320 Ignition/Distributor Engine Speed Input Circuit](https://diagxcar.com/codes/p0320) - [P0326 Knock Sensor 1 Circuit Range/Performance (Bank 1 or Single Sensor)](https://diagxcar.com/codes/p0326) - [P0327 Knock Sensor 1 Circuit Low (Bank 1 or Single Sensor)](https://diagxcar.com/codes/p0327) - [P0332 Knock Sensor 2 Circuit Low (Bank 2)](https://diagxcar.com/codes/p0332) - [P0335 Crankshaft Position Sensor "A" Circuit](https://diagxcar.com/codes/p0335) - [P0336 Crankshaft Position Sensor "A" Circuit Range/Performance](https://diagxcar.com/codes/p0336) - [P0339 Crankshaft Position Sensor "A" Circuit Intermittent](https://diagxcar.com/codes/p0339) - [P0340 Camshaft Position Sensor "A" Circuit (Bank 1 or Single Sensor)](https://diagxcar.com/codes/p0340) - [P0341 Camshaft Position Sensor "A" Circuit Range/Performance (Bank 1 or Single Sensor)](https://diagxcar.com/codes/p0341) ## Symptoms - [Why does my car hesitate when I accelerate?](https://diagxcar.com/symptoms/car-hesitates-when-accelerating) - [Why is my engine knocking?](https://diagxcar.com/symptoms/engine-knocking-noise) ## Repair costs - [Knock sensor replacement cost](https://diagxcar.com/cost/knock-sensor-replacement) --- Source page: https://diagxcar.com/codes/p0325 Updated: 2026-11-03 General information, not a substitute for a qualified mechanic.