Multiple Fault Codes - Ecu Or Wiring?

[filipharvey 0]

After a strange loss of power on Saturday, I've had a load of codes come up related to MAF, Lambda and EVAP control sensors. To me this is too much of a coincidence for all of them to fail at once so I'm going down the lines of wiring loom.

I have disconnected the connector block on the NSF chassis leg which appears to be connected to all of these, and it only brought up on extra fault of the fan circuit - which I expected.

Disconnecting this block makes no difference to the running of the engine. It was fairly corroded on a few of the pins which I have now cleaned up. The faults however are still showing.

Is there anywhere else, other than at the ECU where these items are connected?In case it helps, the fault codes are as follows:

 

P0100 - Mass Air Flow (1) - Signal Low

 

P0443 - EVAP Circuit (4) - Signal Low

 

P0135 - Preheating resistance 1 above catalyst - Signal Low

 

P0155 - Preheating resistance 2 above catalyst - Signal Low

 

P1135 - Preheating resistance 1 above catalyst - Invalid Signal

 

P1155 - Preheating resistance 2 above catalyst - Invalid Signal

 

 

All 4 lambda signals are showing a solid 437mV, whilst the MAF shows 0.000V

 

There have also been errors relating to the throttle position, although these haven't returned since the problem first arose on Saturday.

 

Prior to that, all lambdas were switching correctly, albeit one of the post cat lambdas at a slightly higher voltage. The MAF has always shown correct values too.

Having not had the engine fitted for long, I do check these things regularly to make sure everything is ok.

 

Any chance it could be an earth fault to the ECU? Is it just earthed by its connection to the plenum?

Or would an ECU earth fault mean that the car wouldn't run at all.

 

It may be worth pointing out that the P0135 and P0155 codes will not clear at all, even with the engine off.

[filipharvey 0]

156 with a 3.0 V6 running on an ME3.1 ECU, by the way.

[Bigdar 62]

 

You know who you need anyway

 

[filipharvey 0]

And that's why I'm here!

[Bigdar 62]

Kinda guessed that

[filipharvey 0]

 

Now then, where is the oracle???

[Bigdar 62]

He's on here a lot, and does answer but he's not necessarily on here every day.

 

[filipharvey 0]

Lovely. I'll be patient

[Smaky 73]

How tight are the battery connections?

[filipharvey 0]

Funny you should say that, but the negative terminal is ever so slightly loose. It does seem to make a good connection although you can move it by hand.

[Smaky 73]

loosen it off a little, push down on it as hard as you can then tighten it again.

[filipharvey 0]

Tried that last night and I'm still having the same issues

[Smaky 73]

Mmm, this has to be a connector issue, so many random signals all at once, or at least the ignition flicked itself off for a split second. This sort of thing needs to be dealt with hands on, if you can make the Swindon meet tonight I'll have the laptops.

[filipharvey 0]

Too far for me unfortunately. Do you think its something I could trace with the help of FES? Doesn't matter what I try, the 2 stubborn codes won't clear and the others come back as soon as the engine is revved.

Edited March 7, 2013 by filipharvey

[Smaky 73]

If the MAF is hard then that'll need replacing.

[filipharvey 0]

I'm not sure I get what you mean?

The MAF code resets but comes up again whenever the car is started. Thing is though, 2 days prior to this the only code I had was for one of the rear lambdas, and that was a high signal which I expect to see occasionally as the rear cats have been removed.

As it stands, since I reset the codes after the initial power loss, all power has returned, but I now have a wandering idle when moving with a warm engine, but fine when stopped or cold.

 

Where are the two front lambdas connected, as they are the two codes that will not reset at all. I suspect a common connector between the two may be the cause.

 

Looking at the ECU pin out, the MAF is on the opposing connector to the Lambdas.

 

If I disconnect the plug on the MAF, nothing changes other than I get an additional code relating to the intake air temperature, so at least some of the wiring to the MAF must be ok.

Edited March 8, 2013 by filipharvey

[Smaky 73]

If the intake duct is loose or the multiplug above the thermostat is corroding then you may get the front lambda warnings, both the precat lambdas plugs are in the same location as that too, the post cats are in the box on the rear head next to the ECU, though if the cats are removed then the signals through the ECU can confuse it.

[filipharvey 0]

Checked those too and they all seem to be in good condition. The only plug I've found to be corroded is the multiplug on the near side chassis leg.

Edited March 9, 2013 by filipharvey

[Smaky 73]

How many keys are on your bunch

[filipharvey 0]

Only the one key.

[filipharvey 0]

Well.....

Car refused to start on Saturday and the cooling fans were running constantly on full pelt - no signal from the temp sensor.

After I disconnected most of the connections in the engine bay and at the ECU, it just about managed to fire up. Touching the throttle killed the engine though. I managed to feather the throttle a few times up to around 5k revs - the more I did this, the easier it did it, but idle was lumpy as custard.

I turned it off, restarted it and it ran fine. Reset the codes again and the only two remaining were the original lambda codes. All other codes mentioned in the posts above returned after a drive however.

There were additional codes of 'low signal' along with the 'no signal' that was there before, so I may be getting somewhere. I'm now on occasions getting 0.047v from the MAF at idle

 

I'm still wondering if it is the ECU though, and that when I reconnected the 2 plugs it moved the pins enough to make contact with the PCB, albeit a poor one. I'm assuming there that the issue with the ECU would be dry solder.

[Smaky 73]

VERY rare for an ECU itself to be at fault, more likely the plug on the loom side having pins backing out

[Smaky 73]

Specifically the coolant temp sensor

[filipharvey 0]

I'll have a closer inspection on the weekend and get back to you.

Thanks for your help so far!

[filipharvey 0]

I've finally managed to have a look and all connections at the plugs on the ECU seem fine. I did suspect the ECU's earth because I had relocated it to the bulkhead when I put the 3.0 in, but I made another earth and the same errors continue to show.

Do the MAF and lambdas share an earth/connection elsewhere at all?

 

When I disconnected and reconnected the ECU this time, on first start it would barely run and it ignored any throttle input. Restarted and it ran fine again.

Almost identical to when it lost the signal from the coolant sensor.

 

The list of faults was pretty long this time - I stupidly cleared them after I had made a new earth to see if they would clear without taking note of them.

Again, the lambda and EVAP codes would not clear, yet everything else did. Once again the MAF code came back as soon as the engine was revved.

The other codes (I will make a note next time) only seem to come back on a run - not when parked.

Edited April 3, 2013 by filipharvey