Service engine light

[Tankeryanker]

Been chasing down service engine light problem on wife's 98 4-dr. Code reads 400 (EGR flow). I've cleaned the valve, tube coming from valve, tried Sea Foam cleanet, Techron ect. Tested valve & related vaccum controls, all seem to be working. Any ideas on how to clean out behind the EGR valve other than removing the head, which I really don't want to do unless I have no other choice. Car seems to run OK.
Thanks

[BlazinSaddles]

After cleaning the valve did you reset the computer?

Just disconnect the battery for 5 minutes then reconnect.

[Tankeryanker]

Hi, The code reader resets the light, but it comes back on after 20-30 miles. I'm wondering if there is more carbon & junk inside the passages behind where the EGR valve mounts. I hear that this model has problems with the EGR system.

[BlazinSaddles]

You really should try reseting the computer, nit just the code. There are a lot of other things involved in the EGR system. The EGR valve is controlled by the PCM. Your code is set off by a EGR flow problem, all you are reseting with the scan tool is the problem that the computer detected you are not reseting what caused the problem. It could be that the PCM has "forgotten" how to talk to the EGR and needs to be reset. Unfortunately with the newer systems there isn't a lot that can be diagnosed without special equipment. About all you can do is clean and inspect the physical condition of the system and allow a shop to diagnose larger problems.

I can tell you a little about how it works and maybe that will help you look for problems.

Basically the Exhaust Gas Recirculation (EGR) system lowers combustion temperatures and reduces the amount of oxides of nitrogen formed. It does this by metering the amount of exhaust gases in the induction system and introduces them in to the fuel/air mixture. They are introduced into the fuel/air mixture by the EGR valve. Depending on the vehicle you have three different EGR valve control systems:

1. The EGR valve operates on vacuum and is controlled by the EGR vacuum control solenoid valve which is controlled by the PCM

2. The EGR valve operates on vacuum it is controlled by a flexible diaphram which is spring loaded to hold the valve closed. Vaccum applied to the top of the diaphram overcomes the spring pressure and opens the valve. The EGR valve is under the control of the EGR vacuum regulator valve, which is under the control of the PCM.

3. The EGR valve controls ehaust flow through a single oriffice with a PCM controlled pintle.

If you have system 1 or 2 you can do some testing system 3 will require a service tech.

Systems 1 and 2:

You can test the operation of the valve by manually lifting the EGR valve diaphram, the engine should stall or drastically reduce idle.

If it works check all the vacuum hoses for breaks, leaksor kinks.

If they are okay, disconnect the hose from the egr valve and attach a vacuum pump to the valve. When you apply vacuum the engine should stall or reduce idle. If not replace the valve because this is an indication of a busted diaphram.

Check the operation of the EGR control solenoid, Check for vacuum to the solenoid. If vacuum exists check for battery voltage to the solenoid.

If everything tests okay then you have a control problem (possibly one of the many sensors malfunctioning) and will need to take it to a shop.

[muddflap]

I have a 1996 Geo Tracker engine light does not work will not pass inspection