Engine Management Light Reset ?

June 8, 2008

In an attempt to track down the reason that I am having erratic slow running on my Yaris 1.4 diesel - for which I have placed two recent posts on the subject, I have just disconnected then removed the MAF sensor to see if it looked dirty. I made no attempt at cleaning the sensor, just looked at it then replaced it and replugged it on. I did this with the ignition off but the Battery still connected.

I now have the problem that the engine management light is on. I have tried disconnecting the Battery for 30 mins but this has not cleared it.

Is it likely that just unplugging the sensor has caused this? If so can I clear it myself? I am 100% sure I have not damaged the sensor as I read previously how delicate it is with advice not to touch or poke it in any way - all I did was look.

Reading the forum seems to suggest that in order to get the indication reset I can either get myself an OBD11 analyser at a cost of about £35 or get Mr T to do it at a cost of about £80.

Any comments gratefully received. Thanks.

June 9, 2008

Hi Mate,

There should have been no fault code logged if you unplugged the sensor with the ignition switched off. and in saying that, generally speaking with most toyotas the engine light will extinguish once the fault has been rectified but saving the code in a history log.

am i making sense?

I use a hanatech ultrascan and beleive me it cost a whole lot more that $35......but if they say it will do the job i suppose its worth a shot.

hope that helps a little.

Good luck

Mick

P.S i just read about your other problem sounds like it could be a coolant temp sensor. if this is no good it will offer no cold start enrichment, as it will make the engine computer think it is warm from the get go. best way to check would be to get somebody with a decent scan tool that can stream live data from the ecu, to check the coolant temp reading when cold and monitor any changes. this also could be the cause of the engine light appearing.

June 9, 2008

Hi Mate,
There should have been no fault code logged if you unplugged the sensor with the ignition switched off. and in saying that, generally speaking with most toyotas the engine light will extinguish once the fault has been rectified but saving the code in a history log.
am i making sense?
I use a hanatech ultrascan and beleive me it cost a whole lot more that $35......but if they say it will do the job i suppose its worth a shot.
hope that helps a little.
Good luck
Mick
P.S i just read about your other problem sounds like it could be a coolant temp sensor. if this is no good it will offer no cold start enrichment, as it will make the engine computer think it is warm from the get go. best way to check would be to get somebody with a decent scan tool that can stream live data from the ecu, to check the coolant temp reading when cold and monitor any changes. this also could be the cause of the engine light appearing.

Hi thereand thanks for the suggestions. I will certainly follow up the idea of the coolant sensor. You have got me a bit worried about the management light because if what you have said is true then it suggests the MAF sensor was damaged, or the connections to it by me taking it out and looking at it but I do find it difficult to believe I damaged it. I have never seen the management light on before, only happened when I removed the sensor. One thing I forgot to add is that I did start the car up with the sensor reconnected but not sitting in the hole in the air intake - I wanted to see if that cleared the fault which it seemed to do. It was after I put it back that I noticed the management light up so I assumed that with no air passing across the sensor it had thrown up a fault with the ECU. Having said all this I have been driving the car today and it's exactly the same, a bit blah blah when cold then perfect when warm- except I now have the management light up all the time. I have ordered the simple analyser as the sellers feel confident it will enable me to extinguish the light. If not it's a trip to Mr T as I cannot keep running with the light on as I might get a real fault and not know it. Regards.

June 21, 2008

Hi Mate,
There should have been no fault code logged if you unplugged the sensor with the ignition switched off. and in saying that, generally speaking with most toyotas the engine light will extinguish once the fault has been rectified but saving the code in a history log.
am i making sense?
I use a hanatech ultrascan and beleive me it cost a whole lot more that $35......but if they say it will do the job i suppose its worth a shot.
hope that helps a little.
Good luck
Mick
P.S i just read about your other problem sounds like it could be a coolant temp sensor. if this is no good it will offer no cold start enrichment, as it will make the engine computer think it is warm from the get go. best way to check would be to get somebody with a decent scan tool that can stream live data from the ecu, to check the coolant temp reading when cold and monitor any changes. this also could be the cause of the engine light appearing.
Hi thereand thanks for the suggestions. I will certainly follow up the idea of the coolant sensor. You have got me a bit worried about the management light because if what you have said is true then it suggests the MAF sensor was damaged, or the connections to it by me taking it out and looking at it but I do find it difficult to believe I damaged it. I have never seen the management light on before, only happened when I removed the sensor. One thing I forgot to add is that I did start the car up with the sensor reconnected but not sitting in the hole in the air intake - I wanted to see if that cleared the fault which it seemed to do. It was after I put it back that I noticed the management light up so I assumed that with no air passing across the sensor it had thrown up a fault with the ECU. Having said all this I have been driving the car today and it's exactly the same, a bit blah blah when cold then perfect when warm- except I now have the management light up all the time. I have ordered the simple analyser as the sellers feel confident it will enable me to extinguish the light. If not it's a trip to Mr T as I cannot keep running with the light on as I might get a real fault and not know it. Regards.

Just a follow up for anybody following this one. I did obtain and use the cheapish OBD11 analyser and used it successfully to clear down the engine management light. So obviously for my Toyota at least it proved to me that the fault does get latched into non volatile memory and an analyser seems to be the only way to clear it. Tried disconnecting Battery and removing fuse but none of this works. I now have this little analyser that I can use over and over again and it cost me less than Mr T would have charged to do the reset for me.