What's the check-engine light trying to tell you?

Our tech guru has the answer
by Ferman Lao | Aug 17, 2011

Hi, Ferman!

I have a 2005 Toyota Innova with a 2.5-liter diesel engine and manual transmission. Lately, the check-engine light (CEL) is illuminated when the vehicle is idling in heavy traffic.

The light stays on continuously, even after getting out of traffic. But when it has run continuously without excessive idling, the CEL doesn't light up.

I read in car blogs and forums that one cause of this sign lighting up is a dirty EGR valve. I want to clean this valve myself, but I don't know where this valve located. I hope you can provide pictures.



Hi, Arturo!

The check-engine light in cars comes on for only one reason: the ECU of the vehicle has detected something wrong in your car or one of its myriad of sensors.

When this happens, the ECU can either shut off the engine or go into a "limp home" mode wherein the engine is still running but it is detuned, or is operating below spec performance.

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In these two instances, the check-engine light will come on and stay on.

Sometimes when you restart the engine, the light will go off and the engine will function as normal until the conditions, which resulted in the ECU detecting a possible malfunction, occur again.

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Other times the light will stay on even after you restart the engine. This will require a trip to a service center so proper scan tools can reset the light and ideally fix the problem that's causing it in the first place.

There normally is an associated "trouble code" stored in the ECU's memory. To be able to determine what the trouble code is, one needs the aforementioned scan tool or a diagnostic-trouble-code reader. These can be as simple as code readers, which display a generic OBDII code, to a manufacturer-make and model-specific factory scan tool, which has the ability to test some--if not all--of the a vehicle's EFI components and sub systems.

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And therein lies the catch.

To be able to truly address the problem you would need to know what's causing the light to come on. Perhaps it really is the EGR valve mechanism that's causing the problem, but then again perhaps not. I've taken a look at where the EGR valve is located on the Innova. To get to it would require dismantling the throttle body and parts of the intake system.

EGR in a Toyota Innova

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Given that you are assuming the problem is the EGR based on what you've read in the online forums, and with no affirmative confirmation that it actually is the EGR, I wouldn't advise you to do it yourself.

The only option I can recommend is to have it diagnosed at a service center with the proper tools then work with the pros to resolve your problem. This may mean showing them the discussion forum that you are talking about and giving them as much information about the car as possible.

It's not likely going to be cheap but it's definitely going to be much more cost effective than doing a botched-up DIY effort and needing to replace parts that might be damaged in the process.

Also be aware that what you have in mind is a patch job and that you alone will bear the responsibility of the work that you want to have done--whether it resolves your problem or not. This should be clear to you from the onset, otherwise you will be unfairly asking the service center or mechanic doing the job you have in mind to assume risks that they should not be taking.

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Best regards,

Ferman Lao
Technical Editor

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