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Engine Management Light On No Error or Fault code !


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Ran diags on My 07 Yaris, after MOT failure MIL Light on No reported errors.

Took to Toyota garage £96 later reported the same, wanted to start investigating, alternator, Battery etc, ball park cost £700 parts, then move on to electrical wiring issue.

Alternator replaced, all checks out OK.

RAN some tests and cleared MIL lamp just by clearing logs.

Here's the issue, If I clear the fault then start the engine runs fine, If I turn the ignition off then on within 2 secs MIL lamp remains off, repeated again and again successfully.

If engine off greater than >2-3 secs then MIL lamp returns. No error codes...

Very odd.! any ideas appreciated.



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Hi, Yes its an 07 Yaris 1.4D-D4

MOT Failure is, and I've been told that new GOV Legislation, the EML must be off regardless of the fault codes reported .. Everything else passes...

Legislation for these new rules commenced March 2018, previous to this it would be a pass... MOT pass worth about £2500 - £3000 scrap value / trade in £400 rediculous for Engine light on...Toyota say they would have to start investigating Wiring loom, (Labour charges creeping up)..

So far spent £300 with no results (Alternator was faulty, new Battery, and Toyota Diags £96) Charging is now all fine and working..

Thanks, Stu..

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Try smacking the dash a bit near the cluster, my dads old car had a problem with the wiring somewhere and it would put the oil light on all the time. A good smack fixed it. I really have no clue what else to suggest right now though. Disconnect the bulb so you can get the MOT pass? lol (probably not a good idea)

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Find a decent auto electrician and explain the problem.  There should be certain parameters to bring the MIL on (or to keep it off).  Since you can get the car into both states then someone with the correct diagnostic kit and the knowledge should be able to source which parameter is changing (thus making the light come on) then suggest a fix.

As a side note a few years ago I had a weird fault message on a Ford Focus.  The fault codes couldn't be read by my home reader but it turns out the more professional ones can read 'deeper'.  The codes mainly related to ABS faults, but the auto spark explained (over mobile phone with poor signal so I didn't catch some of what he was saying) that if the computer can't read info from the speedo properly, then it thinks the car is travelling at a different speed to what the ABS sensors are telling it, thus it throws ABS faults.  He did some form of solder repair to the dash pinnacle which cured the problem.  IIRC it cost about £225 or so.

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Well TBH we have had two auto technicians look at the fault at £65 a shot... The last one was called out to help when I was told "It's an MOT failure" so it has to be fixed..

Recommended that I take it too Toyota Garage which I did. Toyota said they would find it they were quite adamant that all the other diagnostics tools used were not specific and probably would not be capable of finding the fault.... 3 Hours later, at £96 a pop! their diagnostics kit came back with the same results, nothing found.

So £220 on Diags and no further forward.. I bought an off the shelf tool and can reset the MIL light by clearing an empty fault code. This remains out, and stays that way providing I turn ignition of and on within a 3 sec period, any longer, it comes on and stays on.. Something must be decaying or fading offline when ignition is off, pressure voltage, Temp, I don't know but a gradual process of elimination. Any thoughts.. New Battery, new alternator (14.2v Charging)

Has anyone got a full list of sensors, maybe with spec..?

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  • 2 weeks later...

Just an update, but no further forward....

All glow plugs showed open cct, so thought I would give last shot...

Change them now OK but still did not clear MIL lamp...

Took the car out maybe a good run would clear and maybe hit the CAT converter and do a regen process, as I thought it may be related to DPF...

Sat at a junction and there was some light smoke coming out the exhaust a bit smelly ..!!

After pulling away the car went into Limp mode when it hit 3000rpm, and the MIL lamp returned, but could replicate this every time... Maybe some where in the emissions, have read about fuel starvation or fuel filter.. So where to go from now... BTW O2 sensors aren't reporting, but I have put this down to my diag reader more than the sensors themselves..

Anyone with any further ideas..?


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You should get o2 short trim or long trim reading with torque pro I think I got some reading with the avensis. If it did go in limp mode than there is a fault. But dealer cannot find fault or auto electrician, so it sounds like a loose connection to a sensor.

I cannot really think of any other ideas but you can buy a fuse checker, and go through all the fuses. I think this should be done with all cars once every few years as regular maintenance.

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