Knock sensor fault code

[MrMater]

Hi all,

First post here so hopefully someone can help. I have a 2000 Colorado 3.4 V6 that has a P0325 fault code. I believe this refers to a knock sensor circuit fault on sensor 1.

The one thing that has me slightly confused is the engine management warning light. I would have thought that if the knock sensor circuit had a fault the warning light would come on straight away as soon as you start the engine.

However, the light only comes on once you have been driving for a few minutes, once the engine has had time to warm up. You can feel the ignition retard just before the light appears and then the engine is pretty gutless. Makes overtaking even slow tractors really interesting

Has anyone ever had this fault on their V6? Did the warning light come on straight away as soon as you turned the key or did it come on a little later like mine? Has anyone had experience of taking the air intake manifold off to get at the sensors and sensor cable?

 

[StarCruiser]

With my knowledge of these things gained from Smart cars ([emoji35]) the ECU can register a fault if it doesn't get what it's expecting. So if you have a poor connection or a sensor problem developing that gives an intermittent fault, the ECU will count the number of problems it sees and if it exceeds a certain number over a set time it goes into limp mode and puts the light on.

Suggestion to try, with the engine off, unplug the sensor, a small, often pan shaped black unit with a bolt through the middle that is bolted on the engine block somewhere (don't know exactly but guessing by your post, under the intake manifold), and check the contacts for corrosion. The sensor can be unbolted and checked for corrosion easily. If necessary the sensor can be changed but there is very little to them to go wrong. If there is corrosion, check the seals on the plug are intact and in the correct alignment. Electrical switch/contact cleaner can help clean these or even unplugging and plugging back in a few times may help. You may be able to do this by feel IF you can get a hand in.

Check your wiring for any damage and if possible check the ECU connectors for the same corrosion but disconnect battery before removing ECU connections.

The above is generic info but should help. I don't think knock sensors are too expensive especially if you enter the number off the sensor into Google or eBay.

Good luck with it and let us know how you get on.

Richard

 

[MrMater]

Richard,

Thanks very much for the reply. From what I can see on the various forums the first thing to check will be the cable that connects to the two sensors. Apparently mice love the V of the engine and have a tendency to nibble on the cable while they are there . As the previous owner was a farmer then this might be the case.

In any event the intake manifold has to come off. No way of getting to the cable or sensors until it's out of the way. Last time I had a go I got to the fuel rails and then chickened out! This will be the first time I've tried to properly tinker with an engine and was concerned I'd damage the rails, as the nuts holding the fuel rail ends in place are properly tight (a banjo, is that right?).

Maybe I need to take a brave pill and man up

 

[StarCruiser]

I don't know this engine, but what you say makes sense re the meeces. My mate had a serious electric shock from mouse chewed cables and thought that was it!!

Is it possible to remove the complete manifold including injectors and fuel rails? The less disturbed the better in my view and plenty of paper towel to bung up holes to stop muck getting in as you go.

I know what you mean about chickening out, I get it too and have to psych myself up sometimes. More often than not because I rely on the vehicle as a daily driver, or the weather looks bad if I don't finish in time or I'm afraid it'll cost far more than I expect or any other excuse not to do it.

Can you get a mirror in behind and under the intake, or a smart phone to take pics and have a look?

 

[MrMater]

Mmmm, the thought of trying to take the manifold off with rails and injectors in place had crossed my mind but I think I still need to crack the union joint first to free off the fuel intake pipe.

No chance with the mirror I'm afraid. Just not enough room. Nothing for it but to just dig deep. It's a proper faff though with all the stuff you have to take off first (front grill, skid plates, radiator after draining, fan, timing belt shroud, top and bottom air intake castings) and that's just to get to the fuel rails

Here's the start:



And here's where I grew feathers that last time:



Under there somewhere is that damn cable! No wonder the local Toyota dealership quoted me a grand in labour for doing the work!

 

[StarCruiser]

Hmmm, not sure what fuel connections there are at the far end but it looks to me like you undo 4 bolts and the whole U of the two fuel rails should lift gently off the injectors. Might be a smidge sticky on the O rings but should prise off gently. I wouldn't bother undoing the banjos at the front unless you really have to and then use a snug fitting ring spanner and tap the other end of it. Probably easier on the far end connections to take the rails off first.

A bit tricky that lot I must say. Probably worth ordering yourself in some inlet gaskets before you do the job.

Oh, word of warning, don't use anything silicone based anywhere near it while it's apart as the O2 sensors in the exhaust turn their toes up if they get so much as a sniff of the stuff.

 

[MrMater]

Thanks for the heads up on the O2 sensors. Going to replace the gaskets on the rocker covers as well while I'm there.

Going to start the process today. I'll let you know how I get on. Deep breath

 

[StarCruiser]

Good luck with it…[emoji6]

 

[MrMater]

Ok, so the deed is done! Thanks for the fuel rail advice Richard, managed to get them off without cracking the banjo joints, although I now have to remember where all the hose connections went

Getting the manifold off was pretty straight forward but wasn't expecting to see what I saw when I got it out of the way:





Not the clearest pictures but the valley of the V had four nice pools of cherry red coolant sitting there . Oh joy.
Checked both knock sensors and cable for continuity. Cable seemed ok and no continuity between the sensor terminal and sensor body (which according to a tech at my local dealer means they're ok). Ordered a new cable anyway to be safe.

So, no further forward on the knock sensor fault and now found a new one! Did wonder where my coolant was going, now I know.

Speaking to the tech at Toyota he advised that the coolant could be coming through from either the metal coolant pipe that you can see in the photos, the air intake gasket at either end of the block or from one or more of the three expansion plugs on top of the block.

I've taken the pipe off and can't see any cracks so hopefully this is ok. I'll need to put some black sealant where the pipe end joins the block as there's no gasket or O ring available, so hopefully the O2 sensors will be ok. The guy at Toyota said I'll need to use some sealant on the air intake gasket as well at either end.

I'm going to bang out the three plugs as well and replace. They're only £6 each and just need Locktite to seal.

Question is, could the coolant have come from anywhere else? Hair line crack in the block??

 

[StarCruiser]

The two areas highlighted look suspect to me. The right mostly as there seems to be connection between the two rectangular holes and then a blackened triangle with a line leading right, towards the red coolant stain that's been there a while. The left looks suspicious too. Personally I wouldn't be disturbing anything that I wasn't totally sure had a problem, re the core plugs.

I would possibly remove that coolant pipe and check and replace its seal. It will probably be fine but worth a check as you're this far in.

Knock sensors will have been affected by all that coolant. Personally I would look at changing them while you're in there as they are such pigs to get to, probably for new ones but look for a number on them and get from the manufacturer (Denso, Bosch, whatever) as they should be cheaper than Toyota but worth asking the dealer anyway. That way you know it's not them at fault and you may just cure the problem.

Well done BTW for keeping the chicken in the coop. [emoji6]

 

[MrMater]

Hi Richard, pictures were a bit misleading. The black triangle was just leftover goo from the gasket. Once cleaned up it was all solid metal (phew).

Left the expansion plugs well alone as you suggested. They seemed solid anyway. Put it all back together today so will stick some fresh coolant in tomorrow and start the old bugger up. Hoping the coolant leak is sorted now but I guess I'll find out when I start him up.

Left the knock sensors in place as I double cheked them again and they seem to be ok. Suspect a problem with the ECU but will test the terminals tomorrow with my multitester. Time will tell.

 

[MrMater]

Update. Started him up, fuel pouring all over the floor . Seals on a couple of the injectors failed when I put them back in. So, £80 later for 12 new tiny O rings and 6 grommets (who knew rubber cost so much) the fuel rails back off, injectors cleaned and fitted with new rubber, back in and assembled. Everything crossed, started up again and no fuel leaks. Phew. Took him for a quick run to check the knock sensor fault, and hey presto, within a few minutes the lights back on. Damn and blast.

So, did the decent thing and cheated! Spliced the knock sensor cable from sensor 2 into sensor 1, bypassing the fault. Took him back out and no light, more importantly no retard on the ignition timing! Hooray.

Richard, seems you were right, the fault was with the knock sensor, despite passing my continuity test. At least I saved myself £160 by using the cheat rather than replacing. Silver linings etc.

So, what have I learned? Don't be afraid to have a go and avoid sprouting feathers. You might make a few mistakes but will probably learn something along the way.

Next thing on the list, sort out the auto gearbox, which is not quite right. Won't be trying to tackle that one myself though! Needs a recon I think.

 

[StarCruiser]

Hey! Well done for finding it and for coping with the fuel leaks.

I'm not sure about the splice though as anything more than proving the fault. I doubt Toyota would put two knock sensors if one would do the job on two banks of cylinders. Although the ECU now thinks it has the right inputs, it is more than likely varying the fuelling on bank 2 based on what it senses for bank 1. Electronic injection varies mixture and spark timing to be the most efficient which is just prior to the point when detonation (otherwise known as pinking) occurs. The knock sensor listens for that pinking and backs things off to avoid it, many times a second. Detonation is something to avoid as it can lead in the long term to permanent engine damage.

In short, you need to change the sensor.…but you were going to do that anyway…right?[emoji6]

 

[MrMater]

Flip. Do I really have to take it all apart again? Thought I'd avoided that!

Oh well, back out with the spanners I guess. Thanks again for the advice. At least I know what to do this time.

 

[StarCruiser]

Sorry, I know how you feel and its part of the learning curve. You might be ok…but then you might not. It's the price you pay for peace of mind. For my money, if you keep to the original, you can't go far wrong. As soon as you deviate then the doubt gremlins creep in and you start worrying if it's going to fail. Toyota put two there for good reason.

Still, you've had it apart a few times now, you won't quite be doing it in your sleep but I bet it'll be apart and back together in no time now. [emoji6]

 

[MrMater]

Thanks Richard. I've had a little think about how I would have approached this if it happened again.

For anyone who comes across either the P0325 or P0330 fault in the future I would suggest trying the knock sensor cable splice first, before you get into the faf of taking off the air intake manifold. If I'd known to do this initially it would have saved me the cost of a new cable and told me the knock sensor was at fault.

For reference, there are three wires going into the connector at the top park of the cable, one black, one grey and one brown. The black and grey ones are the connections to the sensors, black to sensor 1 (P0325 error code) and the grey to sensor 2 (P0330 error code).

Just disconnect the cable at the top end, just behind the timing belt cover on the left hand side as you stand at the front of the engine, snip both the black and grey cables about an inch down from the connector (you need to cut and peel back some of the outer plastic cover, don't touch the brown wire). Strip the insulator from the ends of both cables at the connector side, twist them together and secure into one end of a connector block. For the 0325 fault, strip the grey wire on the sensor cable and connect to the other side of the connector block. For the 0330 fault connect the black instead.

Start up and go for a drive. If your engine warning light no longer comes on, you know your sensor cable is good but the knock sensor is faulty. If the light still comes on it may be the cable so the manifold has to come off. However, I'd wait until you have disconnected the cable from both knock sensors and tested it for continuity before you order a new one.

 

[StarCruiser]

One of the rules of troubleshooting…never replace an item until it is proven faulty.

You have learned well Mr M…

 

[StarCruiser]

Thanks for posting the connection test. That might go to prove the cable to the sensor, or the sensor itself where both are unseen under the manifold.

Did you complete the repair?

 

[MrMater]

Hi Richard, yes all done. He was due a minor service as well so I've changed the oil, filters etc. Did an ATF change as well for good measure. Suprising the difference a basic ATF change makes to the feel of the gearbox, even though the fluid was only 6 months old. Should probably change the gearbox filter as well at some point but shifting the exhaust pipe to get access to the sump is going to be a pig. There's no way the bolts on the clamp are going to come off without a major fight.

 

[StarCruiser]

Nice one MrM. Those feathers are way back in history now. Seems like you've got the bit between your teeth.

I really must change my ATF, I'm told I have no filter in my 81 auto box by my Toyota parts chap so should be straight forward.