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Hiace Check Engine Light


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Hi. I am a new member hopefully looking for a solution to a problem that has defeated me so far. We have a H200 2008 Hiace Commuter that I have converted to a camper. It has done around 195000 kms. Some time ago the engine check light came on and the code reader indicated that the problem was the downstream 02 sensor (code P0038 from memory). So far I have done the following in order: (none of these have fixed it)

  • replaced the downstream 02 sensor with a non-genuine sensor
  • replaced the cat converter (again non-genuine but not a free flow)
  • cleaned the MAF sensor as much as possible from up through the air cleaner box with cleaning fluid (I didn't want to take the entire bumper off to remove it)
  • taken it to a dealer who replaced the 02 sensor again with a genuine one
  • fitted a check engine light eliminator between the downstream O2 sensor and the cat convertor to trick the ECU
  • replaced spark plugs (which badly needed replacing)  in the vain hope that it might have some bearing on the problem

None of these has fixed it. After resetting the codes it comes on again after some 50 or so kms.

I have had it to both dealer and a local workshop who specialise in EFI etc in the hope that they know more than I do and they cannot isolate the problem.

All else seems fine. The engine runs well, doesn't use excessive fuel (although the exhaust smells a bit). We have driven it for several thousand kms as is without any problems at all apart from the CEL being on all the time.

I am now thinking that the problem is possibly in the ECU itself. I am now just ignoring it for the present in the hope that a) it won't get any worse or b) the cause will become evident.

If anyone has any info that might shed some light it would be appreciated. Thanks



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This is a very frustrating scenario for sure. I wonder if the connectors were checked. Usually dirt or some form of contamination can enter the plugs and cause these false codes. Worth checking right ?

I'd unplug any or all connectors and give them a thorough clean and plug back on.

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  • 1 month later...

Hi there. Adam here.

my Hiace seems to be similar.

06 Petrol 2.7 (337 000 kms)

toyota technician said new cat.

I replaced O2 sensors & cat.

Now I’m researching if the EGR &/or tiny leaks may be a thing here.

my CEL comes on if I’m heavier on the right foot for a while, eg with a load in the back & going up long inclines on the freeway.

normal day to day commuting is fine. The light stays off.

twice (in the hills on the freeway) I had to pull over & wait about 40mins for the engine to come good after it wouldn’t accelerate any more.

thought I would need a tow. Black smoke & barely idling without stalling the whole 40 mins.

then after waiting, it all came good. Both times. All of a sudden the revs were clean & the acceleration was fine.

that was before the cat swap.

Now I’m just worried about loading up & going on a road trip again.

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22 hours ago, Adz said:

Black smoke & barely idling without stalling the whole 40 mins.

I would check for any leaks around where the O2 sensors are. Flange gaskets perhaps ? Your O2 sensors are detecting a lean condition and it's fueling it up.

Makes sense when you say under load the CEL comes on. It's more air trying to get in when you're pushing hard. Under light acceleration it's not, so it must be a small area somewhere in that vicinity. 

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In my case even if there were a problem with the EGR or air leaks etc, I have fitted a CEL eliminator which fits between the Cat and the O2 sensor, thus taking the downstream O2 sensor out of the exhaust stream. The signal supplied to the ECU is constant. Apparently they are used for hot motors where the air/fuel mix has been altered so that you don't get the CEL light all the time.

I've given up on it at the moment. Other things to worry about like a water pump.


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  • 7 months later...

For anyone who read my post, and those who answered, about the CEL on all the time with a downstream O2 sensor code (P0138 I think) that I couldn't fix after replacing O2 sensor, CAT and them a CEL eliminator, I decided to leave it and see what eventuated. As it turns out it seems to have been the alternator. We got 3 or 4 thousand kms out of it and on Wednesday the alternator failed making a nasty bearing noise. I replaced the alternator and after a reasonably long run the CEL has not come on again. So it seems like it was a low charge rate. It's now charging at 14.1 and no problems.



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Now that's pretty interesting. Just goes to show that sometimes you can't rely on fault codes alone to figure out the issue. Sometimes it does and in this case, clearly doesn't.

It makes sense though. If the system voltage is down, it can create false triggers on those items that rely heavily on accurate voltage to maintain optimal conditions. The O2 sensors being one such system. 

Thanks for the update Hugh :thumbsup:

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Yes Tony,

I just pulled the alternator apart and the problem is in the overrunning clutch. It overruns both ways so the alternator was not spinning as fast as it should, or in the, end at all, and probably caused a low charging voltage. I should have checked the charging voltage long ago.  Brushes were worn right down as well.

A bit more knowledge! I had no idea they even had an overrunning clutch.



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