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I recently had the check engine light come on again in my 1999 Chevrolet Lumina 3.1L. The code scanner showed a code P0327, which is a knock sensor issue. After researching the code, the three possible causes are a defective knock sensor, faulty wiring or a bad PCM.
Is there a good way to test the knock sensor? Thanks…
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Thanks for the info! I followed the video and here is what I did:
I unplugged the knock sensor connector and then turned the ignition key to “run.” I set my DMM to 20 DCV and inserted the red lead into the connector on the PCM side to get a reference voltage. The black lead was on battery ground. It showed a reading of 0.06 volts.
(Turned the ignition to the “off” position.)
I then did a back probe test. I plugged the knock sensor connector back into the knock sensor. I inserted a pin in the back of the connector. Turned the ignition key to “run.” Set the DMM to 20 DCV. I put the red lead on the pin at the connector and the black lead on battery ground. It showed a reading of 0.06 volts.
(Turned the ignition to the “off” position.)
I also did an ohm scale test on the knock sensor that the shop manual recommended. I set the DMM to 2000K ohm and inserted the red lead into the knock sensor and the black lead to battery ground. It showed a reading of 103K ohms, which was in a specified range (93-107k ohms) in the testing flow chart of the shop manual.
I also noticed that the plastic connector on the knock sensor was a bit loose. When I plugged the connector back into the knock sensor I found that the plastic connector had a little bit of play in it – I could slightly wiggle the plastic connector side to side.
Could this just be a bad plastic connector on the knock sensor? I’m thinking this because it showed the exact same reading on the PCM reference voltage test (0.06 volts) and the back probe test (0.06 volts). It’s like that voltage at the knock sensor plug-in connector is not getting to the knock sensor.
try the ohm test again.this time put both leads on each pin.
see what you read. also wiggle the connector while taking the
reading.see if the ohm reading jumps around. what voltage reading
are you supposed to see with key on engine off. I would think 5 volts?The knock sensor has a single pin connector. To test the ohms again, would I put one lead of the DMM to the knock sensor and the other lead to the knock sensor connector on the PCM side?
I have the GM shop manual for the car, but I can’t find the reference voltage that the PCM sends to the knock sensor. It seems like most cars have 5 volts going to the knock sensor. The readings I was getting was in the 0.05-0.06 volts range. Maybe I don’t have my DMM on the right setting.
I did the ohms test again and it showed 103K ohms on the knock sensor…
Inspecting the knock sensor after removal, I saw the plastic connector on the knock sensor itself was very loose and could be moved from side to side. I replaced the knock sensor and erased the codes. I drove the car and after eight miles the check engine light came back on again. I scanned the codes again and it came up with the same code of P0327.
After installing the new knock sensor, I was still getting the same reading on the reference voltage and back probe test of 0.05-0.06 DCV.
So, I’m back to where I started from… I’m wondering if the reference voltage from the PCM is right. I think the correct reading should be 5 volts going to the knock sensor. Would the next step be to do a continuity test between the knock sensor connector and the PCM? Thanks…
Next step is to ohm the wiring back to the pcm.
we need to find a wiring issue or pcm issue.we should
have a 5 volt reference voltage.I removed the PCM to check for ohms. The knock sensor circuit is located on connector plug C1 at pin 33. I checked the ohms at pin 33 and it showed 4.8K ohms. I also did a continuity check on the wire from the PCM connector to the knock sensor connector. It checked out good. I then installed the PCM and the PCM connectors again and did an ohms test from the knock sensor connector to the PCM. It showed 4.8K ohms.
I did another reference voltage check from the knock sensor connector and I’m still getting the same reading of 0.05 DCV. I’ve also learned if you’re using a low cost DMM, the voltage readings might be incorrect. I’m using an inexpensive Cen-Tech/Harbor Freight DMM, so this might be the problem reading the voltage. I tried using a Fluke 333 DMM, but I get no readings from that meter.
Would 4.8K ohms be the correct ohms at the PCM? Thanks…
I’m not sure of the ohms reading.what I can
tell you is from the knock sensor to the pcm
on ohms we should see 0 or close to zero ohms.
next check the voltage right at the pcm should
be 5v dc.Not all knock sensors work the same. Many produce their own voltage when exposed to a particular ‘frequency’ of noise. Something like a specific engine knock. You really need to find out what the factory manual says for testing that sensor before you commit to replacing the PCM. It could just be a connector issue. You’ve pointed out a few times that you suspect connection issues. If the computer doesn’t get accurate information from the sensor, it will set a code. I would see what you could do to figure out how that sensor is suppose to work and how to properly test it and it’s operation before I purchased anymore parts.
Keep us posted.
Thanks for the info! I took a break from this issue, but I’m trying to troubleshoot this code again… The GM shop manual shows a troubleshooting flow chart for a P0327 code. It also mentions if a crank sensor and cam signal are not present, it may set off the P0327 code.
I just bought an ELM327 unit/cable for my computer. I downloaded some free OBD II software programs and connected the computer to the car. It did work and it showed some basic data, but not the data related to a P0327 code. Can anyone recommend some OBD II software that will read knock sensor, crankshaft sensor and cam sensor data? Or maybe an inexpensive scan tool that will read these sensors…
This might be a tool to look into.
http://www.jbtoolsales.com/actron-cp9599-u-scan-code-reader-tool/#oid=1002_1
Keep in mind that there may not be any knock sensor data per se. It might just be an indication of whether or not the computer senses a knock via the sensor. You may be having an issue where your computer needs a software update OR you need to look into the crank/cam sensor problem. They issue may have nothing to do with the knock sensor. It could be a software issue or some other problem that’s setting the code. I couldn’t find anything with my own search but perhaps you might find other information that I didn’t.
Thanks for everyone’s help on this P0327 code issue…
I recently replaced the PCM computer with another PCM. This was a used PCM that I bought on Ebay that was updated with the latest software and the car’s VIN. The car seemed to idle better with this replacement PCM, but the the check engine light came on after about two miles of driving. I checked the code, and yet again it was the same code that came up – P0327.
Here is an update on what I’ve done so far:
Replaced the knock sensor
Checked the wiring between the knock sensor and PCM (checked out good)
Replaced PCMJust to check the replacement knock sensor, I kept the knock sensor connected to the PCM and disconnected it from the engine block. I then connected a jumper wire to the threaded part of the knock sensor and connected the other end to the battery ground. Drove the car and the check engine light came on after about eight miles – same code, P0327.
I’m not sure where to go from this point. I don’t have any advanced scan tools to use and I’m having a hard time finding a scan tool that would help diagnose a P0327 code.
I read in the GM shop manual that a P0327 can set if there is an issue with the crankshaft positioning sensor. Any ideas on what to look at next? Thanks!
Fred, can you post the freeze frame data for the code set?
I really need to see what the PCM was seeing at the few seconds before and when the code was set.
A P0327 Sets when the PCM sees the reference voltage 95% of the trip time. Normally the knock sensor signal fluctuates above and below the average voltage.
It has 8 conditions that have to be met before the computer will flag a code. An example is the coolant temperature must be above 140 before a test is run on the knock sensor. If the ECT is reading wrong than the computer might run the diagnostic during a time that will set a code. For another example the engine load has to be greater than 45% (since this is the most likely time a engine will knock the computer waits till then to “test” the sensor. If the MAF sensor is out of calibration (bad) or dirty it might report a higher engine load than there actually is. The computer would run the test thinking the motor should be pining when in reality load is much lower than 45% and not likely to ping at all.
I hope I made sense.
Do you know of a scan tool software program that I could use on my computer to get the freeze frame data? I have a ELM327 cable that I can use to connect to the car’s PCM…
[quote=”fredsmythson” post=79444]Do you know of a scan tool software program that I could use on my computer to get the freeze frame data? I have a ELM327 cable that I can use to connect to the car’s PCM…[/quote]
One of the best is PCMSCAN
A little pricey at $170.00http://www.palmerperformance.com/store/product_info.php?cPath=21_28&products_id=28
A little cheaper.
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