XJ XJ6 / XJR6 ( X300 ) 1995-1997

P0400 EGR Valve Code

Old 04-29-2019, 09:08 AM
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Default P0400 EGR Valve Code

Hi Folks, our latest code is a P0400, which translates to an EGR valve issue. It pops up maybe once a week (the boy drives the car maybe 6 hours a week). Where would this be located on a 1996 XJ6 4.0 engine? And what's the difficulty in replacing it? Also, I've read where some have gotten away with just cleaning it. Would that be a possibility? Lastly, could this also be an O2 sensor issue in disguise?



Last edited by BobbyDing; 04-29-2019 at 03:19 PM.
Old 05-06-2019, 01:12 PM
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The EGR valve itself is right behind the throttle assembly on top of the intake. You can find plenty of info here and googling it.

The p0400 code by itself typically means that a flow issue is occurring, and may very well just be a matter of cleaning it up. I literally just completed this on my 97 XJ6 this weekend, as it had the same problem.

After my own trial and error, and reading about other's dealing with it, here is what I would suggest:
1) Carefully detach and remove the EGR temp sensor which is right on the other side of the fuel rail from the EGR valve in the exhaust tubing assembly (which comes from around the back of the block), clean it up (I used a fine wire wheel on my drill), reinstall it.
2) Remove the air intake assembly so you can get access to the inside of the intake manifold and underside of the EGR exhaust gas port that drops straight down into it.
- This is what I should have done, as there was apparently a carbon buildup that was blocking the EGR port from above, that others have described as a ball of carbon. I ended up going through the EGR port under the EGR valve on top, and had apparently allowed the carbon to be sucked into my engine as it was running (not a good idea!).
3) Once you have cleaned out the intake (have a shop vac handy to suck out the crud), remove the EGR valve on top and clean it up, and then clean the port that drops down into the intake. There will be some more crud to sweep out in the intake.

With any luck, this is really the only cleaning you need to do. If the EGR valve appears in good order and cleaning the pintle was easy enough and it is closing nicely and moving freely enough, get a new EGR valve gasket and reinstall the valve. If all else is ok, you should be all good! Many make the mistake of thinking the valve solenoid is the issue and replacing it unnecessarily.

Part of my initial testing was to remove the EGR valve, set is aside while being plugged in still, and starting the car. Mine stayed running fine, which told me the port into the intake was indeed clogged, which was made even more obvious when I started poking around in the port with a close hanger wire, and it poked through the carbon deposit clog, which sent crap into my running engine, thus I recommended getting into the intake to clean it out first, so you don't make this mistake. Luckily my car is still running beautifully now, but it was scary at the time when suddenly it started running rough and chuggy, threw codes and started behaving as I would have expected if there was no clog. Once the clog was completely cleared and I got everything back together properly, trying to run the car with out the EGR valve in place did the expected routine of chugging once then dying.

So that said, you can certainly start by removing the EGR valve and checking the port to see if it is clogged, just be ready to get into the intake to properly clean it out without the carbon deposits going through the engine.

Also note that the EGR valve bolts (2) might be rusted in place. My car has 166k miles on it, and is clean as a whistle but one of the bolts broke without much effort, and I had to drill and tap it (grrr).
The following 3 users liked this post by XJ 4Ever:
Don B (05-06-2019), hjsteadman (06-06-2019), SleekJag12 (05-10-2019)
Old 05-11-2019, 08:28 PM
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Thank you so much for this info! Taking apart the intake and throttle body for cleaning (along with replacing all the hoses and belts) was already on our radar. The EGR valve is also now on the list. Your instructions will help a lot when we reach that point.

This is a really great forum.

Thank you again!

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