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Toyota Previa Low EGR Flow

Q. Hi Vincent, I've been trying to troubleshoot a check engine light on my van and using the internet as a tool. Anyhow I came across your site and wanted to know if you had any advice. We purchased the van, a 1995 Toyota Previa LE, SC, 2WD in April of 2001. Shortly after the "check engine" light came on. After some investigating I found that the van had been in the shop and they had replaced the EGR valve for this very problem.

Toyota Previa Low EGR Flow

On the service order they also suggested cleaning the EGR. So, I took the van to the dealer, and they said the code was low EGR flow and they wanted $300.00 bucks to run a special fuel through it. The whole process took two hours but no guarantee that the light would go out.

I neglected the service because they wouldn't back their work. The mechanic told me I could try blowing out the vacuum hoses. Anyhow, we moved from Texas to North Carolina and the light had went off after blowing out some vacuum hoses, but went back on shortly there after and so I took it to the dealer. (I did try cleaning the hoses but to no avail.)

The code once again was low EGR flow. I took a chance and let them clean it. They charged me $400.00 for the cleaning, once again with no guarantee. Two weeks later, it was back on. Well the light is still on, and the gas mileage is horrible. We're talking 12.5 mpg in the city. We had a 1991 Toyota Previa prior to this one and it got 18 mpg in the city.

Vincent, I hate to take it back to the dealer, I simply can't afford it. (I changed the plugs, rotor, and cap. They did need it) Anyhow, do you have any suggestions?

Thanks,
Tom

A. I have to assume the code is DTC P401 Exhaust Gas Recirculation Flow Insufficient Detected. The exhaust gas recirculation system recirculates exhaust gas, which is controlled to the proper quantity to suit the driving conditions, into the intake air mixture to slow down combustion, reduce the combustion temperature and reduce NOx emissions. The amount of exhaust gas recirculation is regulated by the exhaust gas recirculation vacuum modulator according to the engine load.

If even one of the following conditions is fulfilled, the VSV is turned OFF by a signal from the ECM. This results in atmospheric air acting on the exhaust gas recirculation valve, closing the exhaust gas recirculation valve and shutting off the exhaust gas (exhaust gas recirculation cut-off).

Coolant temperature below 50°C (122°F).
During deceleration (throttle valve closed).
Light engine load (very small amount of intake air).
Engine idling.
Engine speed over 4,200 rpm.
High engine load (very large amount of intake air).

There is a procedure for testing for this code without the use of a scan tool but it is too extensive for me to post here. What I would suggest is to go to the main branch of your public library and go to the reference section. Look in the Mitchell Import service manual and the procedure is in there. You can borrow the book or make photo copies of the pages you need.

Or better yet, if they subscribe to the Mitchell OnDemand or ALLDATA, they can print it out for you from there. You'll need a DVOM meter to do the testing.

Additional Information provided courtesy of ALLDATA

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