[davamanra]

I have been working on my 97 RL and I think I fixed fault code P0401. I used my OBD II reader to reset the code then went out for a test drive. The MIL light never came on but the P0401 code keeps coming back. Is the problem still there or am I not resetting the code correctly? Any info would be appreciated.

 

[Kenso]

Does the MIL work? Meaning does it come on for a few seconds during the bulb check when you turn the key on? Bulb could have been removed by a previous owner.

 

[davamanra]

That's the first thing I checked

I had just replaced that bulb but I wanted to be sure. Turned the key on and the light came on just as it is supposed to.

 

[Kenso]

P0401 is what's known as a 2 trip detection code. Even though the ecu detects it on the first drive cycle, it requires failure detection on 2 consecutive drive cycles to illuminate the MIL. That may be what you're dealing with here.

Also, it's relatively easy to check for proper EGR flow. Connect a handheld vacuum pump to the valve with the car at idle, then apply vacuum to the valve. If the valve opens as it should and the ports are unclogged, the car should stumble or cut off.

 

[davamanra]

EGR valve is good

I checked the EGR valve and it's good, and cleaned the intake pipe. What about the EGR valve solenoid? How do you check that?

 

[Kenso]

You can apply power and ground to the solenoid and it should open allowing air to flow through it. The EGR system usually clogs in a chamber on the back of the intake manifold. Even though you've cleaned out the pipe, the chamber is probably still clogged. That's why I recommend the procedure I mentioned earlier to test for EGR flow. If any of the passages are still clogged it will be obvious that way. There is a DIY on cleaning out the chamber on Legends, the RL is pretty much the same. I wouldn't suspect the solenoid, if it failed you would have an EGR valve lift DTC rather than a flow DTC.

 

[davamanra]

Getting SOME flow through the intake chamber

I'm getting SOME flow through the intake chamber but I'm not sure how much there should be. If the EGR valve is completely open should the engine cut out? When I tested the valve there was a drop in engine RPM but the engine didn't cut out.

 

[Kenso]

If it doesn't cut off it should come darn close. Most times the engine will stall completely, but it depends somewhat on whether the engine is warmed up etc, and how high it is idling at the time you perform the test.

 

[davamanra]

Must still be blocked

I guess the system must still be blocked enough to trip the fault code. I've only done short drives so maybe there hasn't been enough of a trip to fully cycle the EGR system and have the MIL light come on. I'm going to take it on another drive and see if the MIL light comes on.

 

[davamanra]

The MIL light finally did come on

I went out for an extended drive and got the MIL light to come on. Thanks for the info about the 2 trip failure detection, Kenso. It's better to find out that I still have some work to do now than to find out about it later. Now I've got a new problem. After my extended drive I found that I have a leak around the upper pan of my radiator! That's my long weekend shot!! Oh well! Anyway, thanks again for your help, Kenso. I appreciate it.