OK, so while I'm waiting for my new-to-me gearshift assembly to show up (probably tomorrow) in the mail (other thread open for P0705 issue), I've been doing a whole mess of reading, general X308 XJR stuff, some specific trouble codes, etc. Have some questions.

I bought the car knowing it had a check engine light on, seller informed it was for an O2 sensor and I verified the code that it came up with was for the Bank A upper O2 sensor when I inspected the car...code P1646 was what my scanner told me and it specified on the scanner display that 1646 is for the Bank A upper O2 sensor...ok, look at the procedure, easy peasy...arguably the easiest O2 sensor I've ever done.

I'm reading however and I see in another thread that P1646 may only mean the Bank A upper O2 sensor in an XJ8, but in a supercharged car, it may have a different meaning, that being fuel pump 2 relay malfunction...so now I'm second guessing my repairs.

I found the attached AJ27 DTC listing for 2001MY online, and on p48 it says P1646 is the fuel pump relay #2...can I get a definitive ruling on whether its one issue or the other? Fuel pump relay or O2 sensor? If I had a fuel pump relay issue, would the car run adequately on one pump before throwing the DTC? I assume since I've had the battery disconnected for an extended period of time, that the DTCs shuold not be present, correct?

Is there an available pin out diagram for this realy so I can remove it and bench test it and thus eliminate it altogether as a potential issue?

Thanks!

 

For 2001 AJ27, from the Jaguar DTC Summaries:

 

Fiddled around some tongiht. Sifted around looking for the right relay to check, wasn't sure which one it is since Jaguar didn't plan on owners ever servicing their own cars so they never labeled the inside if the fusebox. I checked the manual that came with my car (which is for a 2000 mine is a 2001 of course) and found the fuel pump relay #2 is in the trunk fusebox and the manual says its relay R1...unfortunately the manual also says EVERY relay is R1.

So, can anyone point me at the correct relay for the fuel pumps please? I tried swapping the top and bottom ones, started it, no difference in idle, MIL still on (I didn't scan for codes though which I probably should have), I then put them back in their original spots and then removed first the top one, started it, then shut it down, put that one back in and removed the bottom one and started the car. At all times, the display continued to say restricted performance, but that might be triggered by my dual linear switch problem (along with the gearbox fault message).

Been hunting Google for some clues, all I can seem to find are XJ8 or XKR info, I'm guessing the XKR fusebox may be identically laid out, but I can't know that for sure. I've also seen photos of the fusebox in XJ8 cars and all the same relays are present for them, which they shouldn't be as they don't have secondary fuel pumps. So...confused a bit. Any thoughts?

 

Thanks Stojanovic! This confirms that I misspent $150 on an O2 sensor, but at least I know its new I guess.

Now to track this issue down. Swapping relays from a known good circuit seems like a good place to start, but identifying which is which as well as which fuese are which is necessary before I can do that...blowing up my photo I see numbers next to the fuses so I'm partway there, don't see any for the relays Reasons showns don't list a blown fuse, but is that also a possibility?

Manual says all the relays should be brown, but I see that one black on there...maybe thats the fuel pump relay #2 and this has happened before?

 

Here's the diagram showing the trunk relay box.

The two fuel pump relays get +12V to their coils from Fuse #16 (10A) in the LH Heelboard Fuse Box. However, if this fuse was blown, neither fuel pump would be running. You can try swapping the relay for the Fuel Pump 2 with another one and, if no change, check whether, with the ignition "on", there is +12V on the relay socket No. 1 (86) shown on the drawing below.


If you have +12V on socket 1 (86), and you still get the code, there may be a loss of continuity between the relay socket 2 (85) and the ECM pin EM82-3.

You should download the "XJ Series Sedan 2001 Electrical Guide", search the net for it.

 

Just what I needed, thank you!

I assume the two FP fuses in this box are fed by the relays and go to the hot side if each pump? 7 and 15 or 16 I think they were?

 

Fuse #7 for Pump 1 and Fuse #15 for Pump 2. The fuses are in the "hot" lines from the relays to the pumps so the ECM wouldn't "know" whether they are blown or not. I suggest you also replace the black relay for Pump 1 with a brown one. Even though the code you get is for Pump 2, it might be caused by the black relay if it is different in some way from the brown ones. The codes sometimes don't point exactly to the culprit.

 

I have 12v on pin 86 for both relay sockets when the key is on, swapped the brown relay from FP2 to the socket for FP1 (black relay now out of the box altogether), turned the key and it started right up, let it run for about 5 minutes so the pump is unquestionably running, so the FP2 borwn relay is definitely good.

Will pull the brown relay from the license plate lamp socket and put it in FP2 position and retest a bit later today.

Will the DTC self clear on the first system check when the issue is resolved or does it take 2 drive cycles like it does for the DTC to go active?

 

I do not know whether or when the DTC-s will clear by themselves, you can try disconnecting the battery for at least 2 minutes and reconnecting ("hard reset"). Can you take a picture of the side of the black relay showing its diagram and post it here?

 

Will do this evening when I get home!

Did a little checking yesterday, verified my license plate lights work, took that relay out and put it in the FP#2 position, leaving no relay in the license plate position. Connected the battery, powered on the car but did not start it, checked the codes and now I have an extra bonus code! P1671 showed up, which I haven't looked into yet...I opted to stop at this point because I'm chasing too many separate issues and who knows what I might be introducing by moving from one issue to another while waiting for parts or whatever for the first issue.

So as of now, with the relays swapped around to FP#2 and FP#1 with the original black relay that was there when I got the car, I have P0705 (gearshift dual linear witch problem, used gearshift hopefulyl will arrive today and will resolve this issue), P1671, which is new and undiagnosed and the original P1646 which was present when I bought the car and thought was an oxygen sensor.

All of these codes survive an overnight battery disconnect, so I assume the issues are still present and need to be resolved. I did locate a copy of the electrical manual you recommended so I'll be digging into that for testing with the multimeter and I was going to order up a pair of the proper brown relays so I can replace the black one and either replace the one that was originally in FP#2 position, or I'll have a spare...since the black one is even there, it stands to reason that someone has had to swap out a relay in the past, so having a spare is likely a good idea.

 

Strange, P1671 does not exist for 2001 jag but it shown for 2000 (AJ27 also) and it means - Fuel Pump 2 Relay.

 

Just plain weird. Mine is a very early 01, build date was September of 2000 so maybe some 2000 model year bits got used up when it was built...is there a way for me to check the ECM date or maybe the software version? I wonder if mine might be from a donor car?

Seems like some fuel pump 2 shennanigans definitely going on here...is it possible the pump itself is failed or failing and that might throw those DTCs? Or is it pretty specific to the relays?

 

Your laws say it's 4 warm ups.

 

The ECM only monitors the coil side of the relay, Pins 1 & 2 (or 86 & 85) and will not register pump failure via the pump relay. Pump failure is detected indirectly by detecting lean running at higher engine fuel demands.

The two pumps operate as follows: at ignition switch "on", Pump 2 will run for a couple of seconds; during cranking and after start, Pump 1 runs; at higher fuel demands, Pump 2 joins Pump 1.

You can verify whether the Pump 2 relay is activated by the ECM if you keep your finger on it and have someone switch the ignition "on". If you feel the relay click the moment the ignition is switched "on" and another click a couple of seconds later, then the ECM to Relay 2 communication is good.

As for the pumps, you can test them if you bridge the relay sockets 5 and 3 (30 & 87) and listen for the pump sound. You don't need to have the ignition "on" for this test.

 

Thats great info, thanks very much! Sometimes tracking down a problem is more figuring out what it isn't than what it is. I've got some spade connectors so I'll make up a couple jumper wires and test the pump operation.

Got the diagram of the black relay, see photo below. Appears identical to the brown relay diagram, its a Ford relay and is also rated to 40A, like the brown ones.

Was going to order a couple brown ones, just to swap out both fuel pump relays, or if all else is good keep them as spares.

 

Did a little fiddling yesterday, plugged the battery back in and jumpered the pins on both fuel pump relay sockets (relays out of course), both pumps do operate when I do this. Disconnected battery, swapped the two FP relays so black in #2 and brown in #1, reconnected battery and powered on but didn't start to read codes. Still showing the two FP#2 relay codes, but I noticed they're only active codes, not pending codes. Long-ish shot but maybe one of the pins on the #2 relay just had a bit of corrosion on it and I fixed it just by reseating the relay. I'll spray some contact cleaner in there before I button it back up.

So I cleared them and will see if they return if I'm ever able to resovle my P0705 DL switch problem (have another thread for that) and can drive the car at more than 10 mph.

 

Thank you! this might have just saved me from a rather hot day and an O2 sensor job! Just switched out fuel pump II relay for a good one and no code after clearing.....I'll try a cold start later and see if it comes back, but for now - relaxing with a beer!

 

The code reappeared on cold start, so I’m back to the O2 sensor after lunch.
Going to disconnect and swap the connectors over to see if the fault code follows, if it does then I’ll fit a fresh one.