← Back to list

2001 Chevy 1500 Z71 5.3L Engine P0420 and P0327 Codes: Causes, Diagnosis & Fixes

Model: 2001 Chevy 1500 Z71 Fault Code: P0327 Posted: 2014-10-15 23:29

I own a 2001 Chevrolet 1500 Z71 with a 5.3L V8 engine and approximately 180,000 miles on the odometer. The vehicle exhibits slight smoke during initial startup. A scan tool detected two diagnostic trouble codes: P0420 (Catalytic Converter Efficiency Below Threshold) and P0327 (Knock Sensor Circuit Malfunction — appearing twice). I have previously replaced both knock sensors, but the issue persists. My question is: Does a P0420 code indicate that my catalytic converter has failed? And does a P0327 code mean the knock sensor is faulty? I recently added Seafoam to the fuel and noticed no improvement. I'm wondering if switching to synthetic oil during my next oil change would help reduce startup smoke. Any advice on how to address these codes effectively? Thank you for your time and expertise.

Related fault codes

P0327P0420

Comments (7)

Anonymous 2014-10-16 08:31

Start with the startup smoke issue: > Check engine oil consumption rate — is it around 1 quart every X miles? > Inspect spark plugs — consider replacing with new AC Delco plugs. Are they wet, black, dry, or tan? > Perform a fuel pressure test and observe leak-down at KOEO (engine off). With the OBD2 scanner: examine ECT (Engine Coolant Temperature) and FTP (Fuel Trim) values; compare pre- and post-catalytic converter oxygen sensor readings. Are there any other knock sensor codes? Did you replace both knock sensors? Is there any engine knocking, ticking, or exhaust leaks? Always clear the KAM (Knock Adaptive Memory) when replacing knock sensors — use only OEM-quality parts.

Anonymous 2014-10-23 02:45

Oil consumption is about one quart every two weeks. The spark plugs are dry and tan in color. I haven't yet replaced the knock sensors. There's a slight misfire, no knocking or exhaust leaks. I know I need to replace the spark plugs — I've already found that the oxygen sensor wire cover on the driver’s side is rubbing against the drive shaft and has worn slightly. Additionally, the bottom wiring harness for the shift indicator has come loose and is rubbing against the drive shaft. The plug is chewed up and will be replaced this weekend. Just thought to add: my ignition key switch feels sloppy — I can pull the key out while the engine is running. Could this cause OBD2 trouble codes? Thanks for your help.

Anonymous 2014-10-23 02:48

I currently use a K&N air filter. I’ve heard that wet-type filters may cause oil to accumulate on the MAF sensor — is this accurate?

Anonymous 2014-10-23 09:14

YES — give the K&N filter to someone you don’t like. Always ask why manufacturers don't use this type of filter.

Anonymous 2014-10-27 06:45

Regarding startup smoke: replace the valve stem seals. Over time, these seals dry out and become brittle, which can cause oil to enter the combustion chamber and result in visible smoke during cold starts.

Anonymous 2014-10-29 18:20

Kev2 — you mentioned exhaust leaks. While changing the oil and spark plugs, I noticed two broken exhaust bolts on the driver’s side cylinder head — specifically the outer end bolts at each end. The head appears to be missing; only a stud remains. Could this damaged mounting cause a P0327 code? After replacing the plugs and oil, I cleared the codes and only P0327 returned — P0420 is now gone. Thanks for your insight.

Anonymous 2014-10-30 10:49

This is a challenging scenario — exhaust leaks can potentially trigger knock sensor errors. But how loud are they? Also, note that only one knock sensor (KS1) is reporting an error. A wild idea: erase the RAM memory to reset the learned minimum and maximum knock frequencies. This clears adaptive learning data — compare stored values with actual engine behavior. To do this, disconnect the negative battery cable — all presets and adaptive settings will be cleared, including knock thresholds. This may restore a 'new car' feel. It's free and easy — try it if other diagnostics don’t yield results. Otherwise, proceed to use a DVOM (digital voltmeter) and inspect wiring harnesses for faults.