Reoccurring EML issue

[AndyToyota]

I have a Toyota Prius 2016 4th Generation (new shape).

I noticed the Engine Management Light kept coming on intermittently. Sometimes once a month, once a week or even after every couple of days. 

I had it diagnosed it on a normal diagnostic machine from a local garage & the Fault code kept coming back as ignition coil plugs 1,2,3 & 4 (A,B,C & D).

I changed all 4 Ignition Coil plugs & All 4 Spark Plugs all brand new from Toyota original parts. 

The EML came back on. 

I then took it to straight to Toyota & their diagnostic machine also showed the same faults with the ignition coil plugs but as they had already been changed they recommended I change the cars Auxiliary Battery & replace the hybrid Battery filters as they were quite dirty - I got the work carried out by them.

The EML was STILL ON when I went to pick the car up from them.

Toyota are now saying that they have exhausted all avenues & they can only suggest it’s 1 of 2 things - either the ECU has an issue/needs replacing or the wiring loom leading from the ignition coils to the ECU maybe faulty.

I got a local garage to check the wiring loom to see if there were any signs of any loose connections, cuts or any tampering but there is no sign of this at all, all the wiring looks genuine & clean & untouched/untampered with. 

I find it hard to believe that there is an issue with the ECU & there is no way of testing the old ECU, there is no Auto Electrician in the country that will touch it as it is a hybrid & they simply don’t have the software to test them. Toyota have also said they cannot test the old ECU & even if I replace the old ECU with a new one they will still not guarantee that this will solve the EML issue.

Please can anyone help me??

Do you have any suggestions ? Have you heard of or come across anything like this before with my particular car? It is really important I get to the root of this problem as I have already spent so much time & money on the car & it has still not sorted this issue out & my vehicle is used as a taxi so it is important for work purposes also. 

Look forward to hearing from you.

Many Thanks in advance.

[kithmo]

There was a recall for a fix for possible damage to the engine wiring back in 2018, did yours get the fix ?

Look in the engine bay at the two circled areas in the photo to see if there's any chafing of the wires.

[FROSTYBALLS]

You can use the recall checker to see whether the car has any outstanding recalls - https://www.toyota.co.uk/owners/vehicle-information/recall-checker

[flash22]

Any shop with half a clue will be able to check the coil drivers and narrow down the fault - with engine issue the car need to be put in dyno/service mode with a scan tool

As it's a fault on all plugs it's supply problem, Is anything else not working ?

 

[ian rooke]

Hi as its a 2016 is it not still under warranty 

[flash22]

It should be a 2 wire coil if so you should have 4.5-5v on one wire (brown ? the same colour on all 4) the other will be a pulsed ground (signal from the ecu)

A cam or crank sensor problem may also cause an issue

[FROSTYBALLS]

16 minutes ago, ian rooke said:

Hi as its a 2016 is it not still under warranty 

As the car is used as a taxi, it could have exceeded the mileage limit on the new car warranty.

[AndyToyota]

4 hours ago, kithmo said:

There was a recall for a fix for possible damage to the engine wiring back in 2018, did yours get the fix ?

Look in the engine bay at the two circled areas in the photo to see if there's any chafing of the wires.

Hi kithmo 

Ive just checked & I think the recalls we’re on Gen 3 models - mines a Gen 4 2016 onwards. Plus I’ve been in that link & confirmed my vehicle does not currently have any outstanding recall notices.

i will open the plastic flap & have a look inside to see if the wiring looks different once I get it open 

[AndyToyota]

4 hours ago, FROSTYBALLS said:

You can use the recall checker to see whether the car has any outstanding recalls - https://www.toyota.co.uk/owners/vehicle-information/recall-checker

Thanks frostyballs.

ive just checked on the link I have no outstanding recalls...

[AndyToyota]

4 hours ago, ian rooke said:

Hi as its a 2016 is it not still under warranty 

No literally afew thousand miles over warranty 

it’s on 103k & Toyota are not willing to Stand by & guarantee/confirm that any Further work they carry out On the car Will 100% sort the issue out.  

[AndyToyota]

4 hours ago, flash22 said:

Any shop with half a clue will be able to check the coil drivers and narrow down the fault - with engine issue the car need to be put in dyno/service mode with a scan tool

As it's a fault on all plugs it's supply problem, Is anything else not working ?

 

Hi flash22

ive been to very reputable auto electricians & mechanics (no back street jobs) & they all have failed to find the issue. Also been to Toyota 3 times who are now saying they’ve NEVER seen an issue like it on the Gen 4 models & don’t have the equipment to test ECU’s - if they can’t rest them then what chance have others got. 
All in I’ve spent £1,500 on changing parts trying to find the fault through trial & error:

- 4 x ignition coils (Denso)

- 4 x spark plugs (NGK)

- Water pump & anti freeze

- New Auxiliary Battety 

- New Hybrid Battery Filters 

to replace the ECU now & it still not guarantee to be that problem is too much of a big gamble for me to take.

the car drives fine if it’s only the EML on. But sometimes the dreaded TRIANGLE & flashing warning ⚠️ light saying “go to a dealer” comes on & the car can go into “limp mode” but as soon as I pull over stop & restart the car it resets the car is drivable again but I have to clear the fault code from the system using a diagnostic machine to get rid of any warning lights on the dashboard.

 

 

[AndyToyota]

4 hours ago, flash22 said:

It should be a 2 wire coil if so you should have 4.5-5v on one wire (brown ? the same colour on all 4) the other will be a pulsed ground (signal from the ecu)

A cam or crank sensor problem may also cause an issue

Hi flash22

ok I’ll look into this 

I don’t know if swapping the spark plugs from NGK (as Toyota recommended using) to DENSO spark plugs (the same as the ignition coils) may make any difference...
 

 

 

[Joseph D]

Denso should be the no. 1 choice seeing as Denso is a parts manufacturing company in which Toyota has a financial interest and supplies a huge proportion of Toyota parts for their cars.  NGK is also recommended by Toyota, so, so long as they are the correct model of plug, there should be no reason to suspect anything with either make of plug.

[Joseph D]

I should add, ensure you are buying genuine Denso parts, particularly if buy on eBay/Amazon as there is a plethora of counterfeit parts being sold as genuine.  Especially be cautious of counterfeit Denso spark plugs.  I've seen plugs that were claimed to be Denso Iridium spark plugs where the centre electrode was totally burnt out after only 20,000 miles.  They should last 120,000 miles, go figure.

[AndyToyota]

5 hours ago, Joseph D said:

Denso should be the no. 1 choice seeing as Denso is a parts manufacturing company in which Toyota has a financial interest and supplies a huge proportion of Toyota parts for their cars.  NGK is also recommended by Toyota, so, so long as they are the correct model of plug, there should be no reason to suspect anything with either make of plug.

Hi Joseph D

i always buy genuine original parts from Toyota dealers I won’t buy from anywhere else.

[flash22]

There are a few companies that do ecu repairs they can usually do a fast turn around, just a case of removing it and sending it off, some dealers don't have the staff with the knowledge, most just are following a flow chart on a computer = change the ecu

try.

https://www.ecutesting.com

http://www.ecuexpress.co.uk/

 

[kithmo]

20 hours ago, AndyToyota said:

Hi kithmo 

Ive just checked & I think the recalls we’re on Gen 3 models - mines a Gen 4 2016 onwards. Plus I’ve been in that link & confirmed my vehicle does not currently have any outstanding recall notices.

i will open the plastic flap & have a look inside to see if the wiring looks different once I get it open 

It's definitely a Gen 4 recall, I had it done on mine. What I really meant was to check if any of the wires are chafed there. The recall work wasn't very convincing to me, they just put a bit more tape on and in the wrong place. I ended up taping it up myself and putting a bit of foam over the wires to protect them in the end, as did others.

FYI if the insulation on the wires was damaged when they checked, they should have replaced that part of the loom, I suspect some didn't as it was more involved than taping it up. 

[AndyToyota]

Hey Guys,

sorry for the late reply but I finally got to the root cause of all my EML issues..(showing ignition coil ABCD/1234 on diagnostic)

to cut a long story short my Prius went back to the Toyota Dealership for the 4th time, this time on the back of a AA recovery Truck as the EML issue had gotten so bad the car just wouldn’t move when in gear (start only).

Seems like Toyota now took me a lot seriously than on previous visits & had no choice but to delve deeper into finding the issue & finally found the problem...
It was one poxy little blue wire in the wiring loom coming from the ECU side (going to the ignition coils) - it was literally hanging on by a thread & when they got to the wire it came apart (as per the image I’ve uploaded).

They managed to repair the old wire (obviously at a Toyota Premium cost) but I’m just so glad my nightmare is over, having already spent so much money on it second guessing the issue & changing parts I didn’t have to. Ah well you live & you learn.

Many thanks for all your help & guidance throughout