TWS

iTrader: (62)

Posted this in the GM forum, but it seemed they just talk about PCM tuning there. Not really a maintenance/fault diagnosis forum.

This one doesn't seem exactly spot-on either, but is the closest one as far as I can tell.

Here's the post:

Hey guys,

Need some assistance. My 2001 Silverado 1500HD LQ4/4L80E keeps throwing the code for "Knock sensor bank 2, voltage low". Forgot to write down the DTC #, but that's the explaination.

If trucks are like F-bodies, there is a totally different DTC when the knock sensor itself is going bad. So... I think it may be a wiring issue. I'm thinking perhaps a wire rubbed on something and now is grounding out.

I have done no recent wrenching on the truck. Just happened a couple weeks ago for the first time during a long highway trip and now when I clear the code it throws it again within a couple days.

Anyway, can someone explain to me where I can find the exposed portion of the wiring harness to the knock sensors? Want to check it for visible damage and hook a multimeter up. Would like to start first on whatever portion I can access BEFORE I resort to pulling the intake manifold, etc.

TIA

Country Boy

iTrader: (24)

have you washed the engine recently? I had the same problem with my 04. Drove it for about 2 weeks and the SES went away..

Nick™

iTrader: (2)

the knock sensors are in the EXACT same place as on your LS1 f-body.... the LQ4 is a LS1 based engine. The wire comes out from under then intake and makes a connection at the top rear of the intake where the connector is mounted on a tab. If you've ever removed the intake manifold then it's very possible you crushed the wire under a runner (seen it more than once)

TWS

iTrader: (62)

Ahah! That might be it, except it has been about 4 weeks since I washed the engine and you would think it would have gone away by now.

Here's the deal: just before new year's I sprayed down the valve covers, coil packs and front of intake manifold down with simple green and then rinsed it off after letting it soak in for 15-20 mins. About 2-3 days later, during the middle of a long drive, the SES first came on. Couple days after that, I had the code read and discovered what it was. Since then, in the intervening 4 weeks, I have reset the DTC about 3 times. It has come back each time within a day or two.

I had washed the motor with a wand at the coin operated car wash last summer when I first bought the truck and had no problems. You'd think that would have done it versus this last time when I just used a spray bottle of Simple Green and a few buckets of warm water to rinse the Simple Green off (no water pressure).

I'm leaning towards your diagnosis since the DTC first appeared about 2 days after washing, and I did no wrenching on the truck before the DTC came on. However, if it was due to moisture I think it would have dried out by now.

TWS

iTrader: (62)

Yeah, I'm familiar with the LS1 "family". That's why I was hoping to diagnose it without removing the intake to get at the sensors. It's cold in the garage and I'm lazy.

I'm going to check your suggestion, as that is good advice. However, I hadn't done any work on the motor before the DTC came on.

I think Country Boy's suggestion is the likely cause, it's just that it has persisted for a long time.

Thanks to both of you. I appreciate it.

Country Boy

iTrader: (24)

Its NP. Ive hosed down the motor on the SS many times and never had a problem. Did it once on my truck and I get the SES light I cleared mine a couple times too, but after a couple weeks (2,3 or 4, I dont remember), it went away and never came back.... if it aint broke, I aint fixin it!

thunder550

iTrader: (70)

The knock sensor holes are not sealed well. If you spray down the engine, often water will leak down into the holes and corrode the sensors, causing their resistance (and voltage) to drop. You probably have a bad sensor that needs to be replaced. Bank 2 is the rear sensor. Get a multimeter than reads ohms, find the connector in the back of the intake manifold and unplug it. Measure the resistance across the sensors one at a time by touching one multimeter prong to the pin in the connector, and the other to a clean spot on the valley cover. You should read close to 10K ohms. If one reads significantly lower than that, you have a bad sensor. When you replace it, make a ring of RTV silicone around the knock sensor hole to create a dam to keep water out in the future.

jagjohn2000

sorry to hijack thread, but would the same go for a cam positioning sensor? I changed the sensor with an almost new one and I still get this cam PS code (low voltage)?