FF 37 Diagnostic Code


Hi all:

1994 4.0/6.0 xjs

You likely all know this here but posting for those who may search in need later. This check engine code relates to the EGR valve. I took mine off, cleaned it with throttle body intake cleaner cleaner and put it back on once verifying it still
appeared to work. Easy job. Two bolts and a hose pull. The code will not clear (yet) after 20 minutes of driving thinking of a new one as well as a solenoid replacement could but both easy jobs. Here are the pictures and a video of it uploads.

1 Like

Errrr … that doesn’t look like carburetor cleaner … that stuff is a tad “gentler”, IIRC … :thinking:

1 Like

You are absolutely right. Will edit above. Mechanical brain short on that original post.

Small f/u: thanks to Dallas for editing assistance and 20 plus year diaphragm is done so replacement on the way.

You need to find and download a copy of Jaguar Publication S-91.

The DTCs and explanations of the codes are described.

I have found that FF37 has more to do with the VACUUM ACTUATOR than anything else.

Here is a link to the publication:


I figured Gus would have it because I sent him a DVD FULL of info a decade or two ago.

I would upload it here but it is a large file and not sure it will fit?

All - this is sincerely appreciated. Just what I needed but could not seem to find. Will ease into this fix and post as I venture in so those who are like me can find their ways and those like all of you can reminisce about “all those crazy (not so) scary warning lights and fixes.” Will have to head to support and make a donation in all your names.

Update: got the new valve. Installed it. Disconnected and reconnected battery and? Code is cleared! I actually think the old one is good, but want to slowly replace all the old stuff anyway so really happy here. Appreciate all the help. An aside: Keeping the old part to see if it can’t be restored or of use somehow down the line. Biggest learning experience for this one? Parts are hard to find and not cheap.

1 Like

Yeah it really was surprising to me when I first got my jags, just how little aftermarket support, and even Jaguar support there is for “older” models. Smh

Well, keep an eye on it … I’ve had codes clear like that and suddenly they reappear after days of driving … . :angry:

Will do - agreed, same here but it’s holding up. Today’s “repeat offender” issue is the right passenger side window panel. Works, then randomly sticks up, works, then randomly sticks down. Not for off topic discussion here but I spotted a small “fray” in a wire so hoping for a small “splice and black tape” miracle before I “escalate” it.

I would use a vacuum tester to make sure the diaphram is still good. Even if it shows good sitting on the shelf is going to dry it out over time.