P0327 on GMC: How to Diagnose & Fix
Knock Sensor 1 Circuit Low Input (Bank 1)
2 GMC models · 2 documented issues · $400-$1,100 repair
P0327 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. GM bulletin 02-06-04-023 calls for replacing the corroded rear-bank knock sensor, building an RTV dam around it on the valley cover to divert water, and removing the rear intake manifold foam seal; replace the front sensor and the sub-harness too if they test bad or show corrosion.
Sources for this issue (1)
The 5.3L and 6.0L Vortec engines used in this generation commonly develop knock sensor faults because moisture collects in the valley beneath the intake manifold. Corrosion at the sensors or harness causes persistent P0327/P0332 codes, reduced spark advance, and occasional drivability complaints. This is a well-known GMT800 issue documented in owner forums.
Common Symptoms
- Check engine light
- Persistent P0327 or P0332 knock sensor codes
- Reduced spark advance
- Occasional drivability problems
How to Fix
Scan for knock sensor codes, remove the intake manifold, and inspect both sensors, the sub-harness, and the rubber grommet seals. Replace both knock sensors and the harness together, clean the valley thoroughly, and reseal the sensor wells/grommets to prevent future water intrusion. Many technicians also verify no coolant leaks or cowl water leaks are contributing.
Sources for this issue (2)
P0327 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 P0327 mean on a GMC?
P0327 stands for "Knock Sensor 1 Circuit Low Input (Bank 1)." This code means the knock sensor on engine bank 1 sent a voltage signal that was lower than the expected range. The knock sensor is a small vibration microphone bolted to the engine block that listens for the 'pinging' of abnormal combustion (detonation), letting the computer retard ignition timing to protect the engine. A low-input reading usually points to an electrical problem — a fault in the sensor, its wiring, or connector — rather than actual knock. With the sensor compromised, the engine may run with safer, less efficient timing, causing slightly reduced power or fuel economy. On GMC it is documented across 2 models: Sierra 1500, Yukon XL.
What are the most common causes of P0327?
The most common causes of P0327 are: Faulty knock sensor (Bank 1, Sensor 1), Damaged, shorted-to-ground, or corroded sensor wiring, Loose or corroded sensor connector, Improperly torqued/loose sensor mounting, Open or high-resistance signal circuit, Wiring shielding or grounding problem, Faulty engine control module (PCM) — rare. The specific cause varies by vehicle.
How much does it cost to fix P0327 on a GMC?
Published repair estimates on GMC range from $400 to $1,100 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.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.