MOT - engine management light - does it have to be visible?
Discussion
SS2. said:
The fault log is reporting higher than expected voltage from the heated O2 sensor.
It might be worth clearing the fault codes and disconnecting the affected sensor. If the fault remains high voltage, the problem is between the sensor plug and the ECU. If the fault changes tor low voltage, the problem is most likely to be the sensor itself.
It might be worth clearing the fault codes and disconnecting the affected sensor. If the fault remains high voltage, the problem is between the sensor plug and the ECU. If the fault changes tor low voltage, the problem is most likely to be the sensor itself.
steve-5snwi said:
If you clear the codes and the light goes off how long does the light stay off for ? if its 10 miles or so book the car in for an MOT, clear it in the carpark and prey it doesn't come on while being tested.
If you disconnect the sensor does the code change ?
At the moment the light comes back on as the car starts to come up to temp. I can't drive it anywhere so am restricted to idling on the drive, it appeared after about 10 minutes. If you disconnect the sensor does the code change ?
I really don't do electrical stuff so hadn't fully understood the nature of the fault, hence me changing the sensor twice (the first was a cheap Chinese one so I presumed it was rubbish, the second a Bosch one). It's not a car that's worth much so I'm trying to save where I can as I need the money from the sale to get my Saab back on the road.
Based on your much appreciated replies I'll try things disconnected and also pay more attention to the sensor readings from Torque when it's connected to the reader.
Cheers!
Edited by thetapeworm on Wednesday 26th December 19:39
Athlon said:
Wrong, sorry.
1.1.13 Brake linings and pads
Some brake pads have metal wear indicators so that when the pads become excessively worn the metal indicator touches the disc making a squealing sound. Other pads may have a cut, which if worn away indicates that the pad must be replaced.
No mention of lights that I can see.
Well what am I missing here under 'new failures'?1.1.13 Brake linings and pads
Some brake pads have metal wear indicators so that when the pads become excessively worn the metal indicator touches the disc making a squealing sound. Other pads may have a cut, which if worn away indicates that the pad must be replaced.
No mention of lights that I can see.
https://www.gov.uk/government/publications/mot-cha...
Patrick Bateman said:
Well what am I missing here under 'new failures'?
https://www.gov.uk/government/publications/mot-cha...
You are missing the fact that the manual gets updated all the time, when the new test came out many of the testers complained about the wording for some things and asked for clarification, this was one as well as contaminated brake fluid which is a fail but un-testable! there are others but that's for another day.https://www.gov.uk/government/publications/mot-cha...
My quote was from the current testing guide we use, the light was not really testable as it can also show handbrake on on some cars etc etc.
Athlon said:
You are missing the fact that the manual gets updated all the time, when the new test came out many of the testers complained about the wording for some things and asked for clarification, this was one as well as contaminated brake fluid which is a fail but un-testable! there are others but that's for another day.
My quote was from the current testing guide we use, the light was not really testable as it can also show handbrake on on some cars etc etc.
Well that's good then, glad some common sense prevailed. Where can you find the latest info because I'd have thought that should have been updated on the government site. My quote was from the current testing guide we use, the light was not really testable as it can also show handbrake on on some cars etc etc.
Patrick Bateman said:
Well that's good then, glad some common sense prevailed. Where can you find the latest info because I'd have thought that should have been updated on the government site.
Testers guidePatrick Bateman said:
Athlon said:
Wrong, sorry.
1.1.13 Brake linings and pads
Some brake pads have metal wear indicators so that when the pads become excessively worn the metal indicator touches the disc making a squealing sound. Other pads may have a cut, which if worn away indicates that the pad must be replaced.
No mention of lights that I can see.
Well what am I missing here under 'new failures'?1.1.13 Brake linings and pads
Some brake pads have metal wear indicators so that when the pads become excessively worn the metal indicator touches the disc making a squealing sound. Other pads may have a cut, which if worn away indicates that the pad must be replaced.
No mention of lights that I can see.
https://www.gov.uk/government/publications/mot-cha...
Brake pad wear light illumination is not mentioned in the minor/major/dangerous BUT it does seem an odd omission as it's a wear indicator that activates when the wire in the pads wears though creating the circuit so I would have thought it falls into the category of 'Brake lining or pad worn down to wear indicator' which is a Major.
As ever, I stand to be corrected!
ETA. Just read Athlon's post above which has appeared whilst I was composing this missive & the penny has dropped!
As the OP's car is a 2002 he might want to check the check MIL lights dates in the manual.
Edited by paintman on Wednesday 26th December 20:10
Muddle238 said:
Ridiculous MOT rules, an EML covers a range of potential issues, often caused by a faulty sensor. How a faulty sensor translates into a major fault, which should deem it unroadworthy I do not know. I'm convinced it's all political tactics to get older vehicles off the road and more people into brand new cars for whatever reason.
The function of the EML is precisely defined in law (becoming generally more precisely defined as time has gone by). (For cars) It indicates a fault in a legally-prescribed emissions control system, although it is also allowed to indicate emergency limp-home mode, or similar emergency engine operation.The reason for the testing as part of the MOT is to ensure that vehicles are not producing emissions substantially outside their type approval. One of the issues is that measurement of emissions at the levels required by regulations during type approval is extremely challenging (it's not just a matter of sticking a probe up the tail pipe).
Health effects from vehicle emissions are an important problem, and from published statistics at least as important as KSI due to collisions. It's not particularly unreasonable to insist on emissions inspection, and as the car itself is equipped with sophisticated monitoring systems, it is the pragmatic solution to simply observe the result of the on board diagnostics system.
Muddle238 said:
Ridiculous MOT rules, an EML covers a range of potential issues, often caused by a faulty sensor. How a faulty sensor translates into a major fault, which should deem it unroadworthy I do not know. I'm convinced it's all political tactics to get older vehicles off the road and more people into brand new cars for whatever reason.
Or quite simply the EML means the engine no longer complies with emissions regulations (by as you say, a number of different things - a Lambda sensor failure means it goes in to open loop control, therefore more polluting), therefore not allowed on the road. But keep up your conspiracy theories.
WatchfulEye said:
The function of the EML is precisely defined in law (becoming generally more precisely defined as time has gone by). (For cars) It indicates a fault in a legally-prescribed emissions control system, although it is also allowed to indicate emergency limp-home mode, or similar emergency engine operation.
Has this always been the case though? I know that it is a feature of many Subarus (including my 2005 Outback), that they will put the EML on (plus turn traction control off, and blink the cruise control light), when the car logs any fault whatsoever. A common reason for it is that it thinks the fuel filler cap is loose. Mine has been doing it intermittently for a while, and rather annoyingly when my friendly local mechanic plugged his super-duper code reader in there weren't any error codes logged at all! It seems to happen when it thinks it is low on oil but I can't be 100% sure - I've previously not really cared as it makes no difference whatsoever to the way the car drives, but if it could fail the MOT due to some phantom error code causing the check engine light to light up, well that's a bit of a pain in the arse.Roger Irrelevant said:
Has this always been the case though? I know that it is a feature of many Subarus (including my 2005 Outback), that they will put the EML on (plus turn traction control off, and blink the cruise control light), when the car logs any fault whatsoever. A common reason for it is that it thinks the fuel filler cap is loose. Mine has been doing it intermittently for a while, and rather annoyingly when my friendly local mechanic plugged his super-duper code reader in there weren't any error codes logged at all! It seems to happen when it thinks it is low on oil but I can't be 100% sure - I've previously not really cared as it makes no difference whatsoever to the way the car drives, but if it could fail the MOT due to some phantom error code causing the check engine light to light up, well that's a bit of a pain in the arse.
There have been changes as to exactly what the minimum requirements have been, but the EML has always been a legally mandated emissions system indicator.However, in practice, there are many interacting systems which can affect emissions - fuel and air metering, catalyst monitoring, variable valve timing, ignition, misfires, fuel evaporation from the tank, etc. Almost anything which has potential to degrade emissions (e.g. intake manifold runners) is supposed to turn on the light. As the systems are so interlinked, there are a huge number of potential faults which fall into the category where turning on the light is mandatory. (and just for avoidance of doubt, as fuel evaporation is a regulated emission, a loose fuel filler cap is a fault which must specifically be detected and trigger the EML).
There is some variation between manufacturers as to what exactly they regard as "emergency" operation - e.g. a missing sensor signal. Similarly, especially on older cars, if the ECU had logged a fault code, then the traction control/ESP system would set its own fault code in sympathy (presumably on the basis that when the ECU is operating under fault conditions, torque control requests might not be available). This has been particularly the case on some older Japanese cars, where the entire dash lights up like a christmas tree because you've left the fuel cap loose, even though this should not affect engine running, or capability to alter torque in response to a TC request. I haven't seen what happens in recent stuff.
Roger Irrelevant said:
rather annoyingly when my friendly local mechanic plugged his super-duper code reader in there weren't any error codes logged at all!
Not all readers pick up all codes, you need a more super-duper code reader.More generally, for someone with a hobby interest in electronics it would be trivial to make a timing circuit to light a bulb for a few seconds after initial power on.
Warby80 said:
JimSuperSix said:
Graunching_dave said:
zixujo said:
IF. Sounds like you take your cars to the wrong people. My tester would pass it regardless.
Sounds like your tester is a 
. I don’t want you or your potentially faulty vehicle driving anywhere near me.
over-reacting much?
OP, looks to me like you need to be looking at the wiring associated with the pre cat o2 sensor…
Edited by 98elise on Friday 28th December 09:41
mighty kitten said:
If the original , first and second replacement pre cat 02 sensors are all reporting a high voltage ie rich mixture that’s the issue not the sensor . Mass air flow Meter rarely gives any useful codes on early systems if it’s faulty
Just want to make sure that this useful post isnt lost in the arguments over mot rules...98elise said:
Much of the MOT is not about the roadworthiness of the car. A MIL light on does not render a car unroadworthy, same goes for the airbag warning light (currently on in our car).
Doesn't the airbag warning light being on indicate a (potential) fault in the system and thus if the light is on the system is inhibited and won't fire in an accident? Surely that's worthy of a fail?
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