MIL light

Post by **simon** » Mon Mar 19, 2007 12:55 am

colin adams wrote:(free despite the fact we had by then gone out of warantee)

If the original fault was reported under warranty and still not fixed by the time the warranty expired you are still covered

Novice Racer · Post by **Novice Racer** » Tue Mar 20, 2007 12:53 am

Right folks - update on the MIL situation after an enjoyable visit to Andy G tonight.

History of the problem is that the MIL light came on immediately following fitting my Larini with Robin. Was a JPS last w/e and Dan thought the fault lay with the post-cat sensor (don't have the codes) and swapped the sensor and turned the light off.

Light came on again before leaving JPS and has remained on since. Andy kindly agreed to look at this with the software he has and diagnosed the following codes:

P0138 - O2 sensor circuit high voltage

P0141 - O2 sensor heater (?) circuit

Light put out and left Andy's. Light came on within about 1 min - turned back and attached car to gaget again........

Same fault codes, light back off

Funny thing was that when ignition turned on when car hot, temp reading came up as 108 C for a few seconds before changing immediately down to 87 C (usual running temp) just before I turned the engine over. Switched off and on again - however, this did not repeat.

But it happened again when I got home.....temp 105 C this time after turning on ignition a few seconds following turning off after the car had been running, but could not replicate this on multiple on/offs after this. I think this might have always happened as I have vague memories of this happening from before (but rarely have needed to start/stop engine after just after running it). However, cannot be 100% sure if it is related to current MIL problem......

Over to Robin at alia.......

NR

robin · Post by **robin** » Tue Mar 20, 2007 8:36 am

Ignore the bogus temp reading on display - I am 90% sure that will turn out to be down to the way the ECU samples and filters the engine temp before sending the signal on to the display - basically it's a rolling average of the last N samples, and it may be that this doesn't get cleared properly if the ECU is switched off and back on again within a few seconds.

Provided the temp reads correct after a few seconds of engine off ignition on, you're fine.

As to the codes ...

They indicate a wiring fault most likely - I wonder if when we disconnected and reconnected the secondary O2 sensor we either damaged the wiring or the connector. Now Dan has replaced the second 02 sensor, which will then include all the wiring up to the connector that is near the ECU, so it must be on the ECU side of that connector that the problem lies.

A multi-meter test is required to make any progress - we need to establish that the signals are running properly from the ECU to the post-connector wires and that they aren't shorted to anything.

In the worst case this could also be an ECU fault, but more likely to be a wiring fault.

Cheers,
Robin

kenny · Post by **kenny** » Tue Mar 20, 2007 9:03 am

Same fault codes as mine, replaced the lambda sensor this weekend and all is well

MacK · Post by **MacK** » Tue Mar 20, 2007 9:07 am

Novice Racer wrote:Funny thing was that when ignition turned on when car hot, temp reading came up as 108 C for a few seconds before changing immediately down to 87 C (usual running temp) just before I turned the engine over. Switched off and on again - however, this did not repeat.

But it happened again when I got home.....temp 105 C this time after turning on ignition a few seconds following turning off after the car had been running, but could not replicate this on multiple on/offs after this. I think this might have always happened as I have vague memories of this happening from before (but rarely have needed to start/stop engine after just after running it). However, cannot be 100% sure if it is related to current MIL problem......

Over to Robin at alia.......

NR

I get similar obscure temps for a second, sometimes, when starting the car when hot, or even a few hours after it being hot.

Novice Racer · Post by **Novice Racer** » Tue Mar 20, 2007 11:31 am

Many thanks for setting my mind at ease regarding the temp reading.

Robin, I have a slight suspicion regarding my lamda sensor problem and I will call you to discuss.......

NR

Andy G · Post by **Andy G** » Tue Mar 20, 2007 1:26 pm

kenny wrote:Same fault codes as mine, replaced the lambda sensor this weekend and all is well

Pleased to hear mate - thought they were the same but wasn't 100% sure

mac · Post by **mac** » Tue Mar 20, 2007 2:22 pm

I'm fairly sure that the sensor heating controlled by the MFRU - perhaps it's worth swapping that over with a known good 'un?

Mac

Novice Racer · Post by **Novice Racer** » Tue Mar 20, 2007 10:41 pm

MIL light straight back on today, as soon as the engine started.

It looks like I will need to take Robin's advice and look for problems from the post cat O2 sensor to the ECU.

NR

robin · Post by **robin** » Wed Mar 21, 2007 8:20 am

mac wrote:I'm fairly sure that the sensor heating controlled by the MFRU - perhaps it's worth swapping that over with a known good 'un?

Mac

No. The sensor heater is common with just about every other inductive load from the MFRU - i.e. if the MFRU were the problem then the injectors, ignition coils, etc., wouldn't be working either.

Cheers,
Robin

Lawrence · Post by **Lawrence** » Wed Mar 21, 2007 9:43 am

robin wrote:
mac wrote:I'm fairly sure that the sensor heating controlled by the MFRU - perhaps it's worth swapping that over with a known good 'un?

Mac
No. The sensor heater is common with just about every other inductive load from the MFRU - i.e. if the MFRU were the problem then the injectors, ignition coils, etc., wouldn't be working either.

Cheers,
Robin

Surely the lambda heater has it's own relay and therefore could be faulty, although that would involve a coincidental failure rather than a more likely induced failure.

mac · Post by **mac** » Wed Mar 21, 2007 10:28 am

I thought there was more than one relay in the MFRU.

Mac

robin · Post by **robin** » Wed Mar 21, 2007 7:31 pm

The Lambda heater is commoned on the live side through the same part of the MFRU as the injectors, etc. The MFRU does contain four relays IIRC, but only one of them is responsible for this feed ...

The Lamda heater is then controlled by the ECU connecting the other side to earth. This happens via some type of transistor, rather than a relay, and the transistor is embedded inside the ECU.

Hence if the heater isn't working and you think it's not a lambda sensor failure and not a cabling fault you are left with the possibility that the ECU is faulty

Cheers,
Robin

P.S. There are just three relays in the MFRU and these are:

Start Relay.
Engine Control Relay (main supply to ECU and all the inductive loads).
Fuel Pump Relay.

The later S2 K-series wiring diagrams don't have the MFRU highlighted, though the relays still exist - I don't know if that's because the MFRU has been eliminated on the later cars - I don't think so (if I could be bothered I would go out to the garage and look

).