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Skyvisions, ASE Certified Technician
Category: Toyota
Satisfied Customers: 14417
Experience:  Toyota Master Diagnostic
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Toyota Tercel DX: Check engine light on, 1995 Tercel, 1.5 liter.

Customer Question

Check engine light on, 1995 Tercel, 1.5 liter. Code is reading EGR valve. Had valve replaced 2 months ago. Check engine light back on again with the same code.
Car has 91,000 on it, with new plugs & wires, and new battery. 2 mechanics have told me they fixed it (no explanation how), but still returns within 10 miles of driving.
Would appreciate any further advice. I did the gas cap check also. I'm really frustrated.
Submitted: 5 years ago.
Category: Toyota
Expert:  Skyvisions replied 5 years ago.

Thank you for choosing JustAnswer and allowing me to help you resolve your Toyota questions!


Do you have the Code number?

Customer: replied 5 years ago.
No, just that the all the mechanics have said it's reading the EGR code
Expert:  Skyvisions replied 5 years ago.
There are two possibilities here. The first one is insufficient flow which sets a P0401 code and an excessive flow which sets a P0402 code. 90% of the time it is a P0401 insufficient flow. This is fairly easy to check. At the EGR valve there is a single vacuum line. Disconnect this single vacuum line and apply vacuum to the top of the EGR valve while the engine is idling. If you do not have a hand vacuum pump you can simply apply vacuum by sucking on the vacuum line with your mouth. It does not require a lot of vacuum pressure to open this valve. The engine should run rough and stall immediately. If it does not stall whoever changed the EGR valve or attempted to fix it did not clean the carbon from the intake passage and it is plugged. Let me know the results of this test.
Customer: replied 5 years ago.
I thought there was about 3 vacuum lines on the EGR? How do I determine which vacuum line it is
Expert:  Skyvisions replied 5 years ago.
The EGR vacuum modulator which is a black plastic round device has three vacuum lines going to it. The single vacuum line coming off the one side goes directly over to the EGR valve. The EGR valve is the metal canister with this one single vacuum line. If you disconnect the vacuum line at the modulator and apply vacuum by sucking on this line going to the EGR valve it should stall as I indicated previously.
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Expert:  Skyvisions replied 5 years ago.
I also forgot to mention there is a vacuum switching valve that is designed to bleed vacuum off of this line going between the modulator and the EGR valve so that it does not apply until the computer commands it to. If this vacuum switching valves is stuck in the open position it will not apply vacuum to the EGR valve. If you bypass this vacuum switching valve and go directly from the modulator over to the EGR valve then go drive the vehicle and the problem goes away then you know the vacuum switching valve is bad.