00 I30 P0325/knock sensor question

[MiracleMax]

Hi, everybody!

New to NICO, and can't seem to find a clear answer to this after reading/searching ...

I had me 2000 I30 (95k+ miles) serviced by the dealer a few months back and they found P1320, P0325, and P0302 codes. They replaced the #2 ignition coil to correct codes P1320 and P0302 (and cleared DTC codes). They also wanted to replace the knock sensor (KS), but I asked them not to do that at the time. Since then, I got a scanner/logger, but haven't seen the P0325 code pop up again. Should the P0325 code pop up again if there is a real issue with the KS, or does it only show up once (and presumably the ECM ignores the KSfrom then on and puts the engine in "limp" mode)?

I've also disconnected the battery once since then, when trying to test KS resistance through related ECM pin 93 and engine ground (Engine Control Manual procedure) ... but still no P0325. I'm not confident in the results of that test (lower than the ~550kOhm range) since I had a rather make-shift connection to ground. I've seen some info for how to test the knock sensor (resistance should be ~550kOhm) in the engine bay but I'm not 100% sure which cable leads to the knock sensor. Does anyone have a link to a photo of the 00 I30 KS cable/connector in the engine bay?

Thanks!

[loystock]

P0325 fault code is generated when an abnormally high/low voltage from the KS is detected by the ECM. Nominal voltage is @ 2.5V at Idle but goes up when misfire/pre-ignition/knocking occurs and goes down if there is a loose connection or poor grounding. Most likely, the code was triggered when you had a misfire (P0302).

The KS uses a piezoelectric element (similar to audio tweeters) which generates voltage when pressure/vibration is applied (or sound when electrical power is applied). So when the engine knocks due to misfire/pre-ignition, it sends a higher voltage to the ECM and then the ECM retards ignition timing to avoid knocking. Unlike other sensors which use 2-trip logic to trigger a fault, the KS uses a 1-trip logic. A fault is stored but the CEL is not turned on by KS problem. With the source of misfire gone and assuming the KS and harness are good, you cannot get that fault code again.

Since you have already done resistance measurement (ECM Pin 93 to chassis ground, 500-620K-ohm), you can also check the nominal voltage (@ 2.5V). The KS is mounted on top of the engine, under the intake plenum. The sensor has 2 pins but only Pin 1 (white wire) is used (ground is made when it's bolted to the engine). In the 99 I30 (similar engine to 00 I30), the KS and harness are located closer to the TB (throttle body). Make sure the main engine harness ground points (2 ea near oil filler cap) are clean and tight. Better yet, disconnect and clean them and then apply dielectric grease. A poor grounding can give starting/stalling/misfire problems.

One more thing, the plastic housing of the KS may be cracked and the problem may manifest only when the engine is hot. The resistance measurement may be good even with a cracked housing.