Hi Folks,

I have a CEL and P1646. That indicates a fuel pump relay is about to go in the rear relay box. Correct?

In a the 4.0 V-8 is there only one sub fuel pump relay or are there two? I have been poking around the forum and it seems that a V-8 base has one. Superchargers have two.

Which is relay to replace? The guide in the factory car care manual indicates R4. But which relay is R 4? Is that the only one to replace and where is it. One drawing I say said the fourth from the right. Photo attached. Sorry they are so large.

And which relay brand hold up longest? Any advice?

Thanks

Here the direcriton for R4 relay.

Here's my rear fuse and relay box. Which is R 4?

 

If the fuel pump relay is iffy and fails to close by command you can directly power the # 1 fuel pump by jumpering at the socket 3 ( battery ) to 5 ( to the pump fuse / motor ) with a medium gage wire with blade type wire ends ( best current )

This jumper connection will be hot at all times and drain battery with keys in pocket

The auto parts store can sometimes make one for you from parts box behind cash register if asked

This can save you a tow expense and get you home in some cases

If the engine ECM is picking up the power contacts inside the relay are arcing , arcing is a sign the pump motor is on the way out , you can cut open the relay and do some investigation and have a pump on the way , the pump motor connector can arc also

 

Thanks, Parker 7. I replaced he relay and the CEL code went away. But you suggest the fuel pump is on the way out. Do you have a part number for the pump and where to get it?

 

https://www.britishparts.co.uk/class...3866-jaguar-v8

 

Parts Geek, Amazon, Rock Auto (my choice), Advance Auto Parts, Riley all can provide.

R4 is the relay just before the top of the T. Where # 1 is in Parker's diagram: maybe spray some electronics cleaner in the receptacle (might have been dirty connectors -- it is an old car!).

Attached is the update Handbook which corrects the relay numbering

 

Thanks, Park7, Vauxi and Jhartz,

Are you all of the opinion that the fuel pump relay is indicating that the fuel pump itself is about to give it up? It was replaced about 15 years ago. Would you wait or replace it now.

LA

 

Try cleaning the connections first.

WAIT

WTF:The P1646Jaguar code refers to a malfunction in the HO2 (heated oxygen) sensor control for Bank 1, specifically the upstream sensor. The oxygen sensor is a crucial component in the vehicle's emissions system, responsible for monitoring the oxygen levels in the exhaust gases to ensure optimal fuel use.

How did you get the fuel pump relay . . . ? Oh: maybe from that 2003 Engine Management training course . . . ?

Try this for codes (or Google)





The good news is the Bank 1 sensor is on the right side and fairly easy to get to.

 

For some reason the DTC summary differs for the early (up to MY2000) from 2001 to 2003.(the 2001 to 2003 cars are the same)

 

I would guess for the same reason that early edition of the Handbooks have errors: See #1 versus the relay layout in the Supplement. Lots of errors in some of these Jag documents (QC problem outside of the vehicles themselves). Which begs the question: what is the fault for P1646? Test equipment directories and Google and my independent and two cars that have had P1646, it is an exhaust sensor . . . not Fuel Pump relay.

I am reminded of a story I heard years ago from a major Jag OEM supplier (TRW VP responsible for supplying parts to the Honda Marysville OH plant) while we were discussing Jaguars (I had just bought a new 2000 S-Type) that he had heard from a Ford Exec: "Trouble with Jag engineers is they get a couple of cars out of Brown's Lane -- and unlike these Japanese -- they pat themselves on the back and drink tea for a couple of years."

 

If you DO NOT have a supercharged XJ, then I would discount the FUEL PUMP RELAY #2 (not installed) and concentrate on the HO2 sensor.
Unplug the 'A'bank UPSTREAM sensor and see what DTC you get?

 

I do not have a supercharged XJ8.

I have a 2001 XJ8 naturally-aspirated assembled in Dec 2000.

If it is not the one fuel pump relay, why did the code not come back after the relay was replaced and the car restarted a few times?

My mechanic's diagosotic box is a 2.

If I disconnect the HO2 sensor, what should I expect?

 

You're misreading the previous post.

Supercharged cars have TWO fuel pump relays, hence Relay #2 is not installed.
N/A cars only have a single fuel pump relay, as they only have a single fuel pump.

 

If the code P1646 did not come back after a few miles and restarts, pack it up, you're good. If it does, IT IS NOT A FUEL PUMP RELAY ISSUE, it is the right hand exhaust sensor.


But I have to ask: What does "My mechanic's diagnostic box is a 2," mean?

 

Meaning the OBD II scanner though this one is a large rectangular box as large as a laptop.

 

Meaning the OBD II scanner though this one is a large rectangular box as large as a laptop.

 

WDS ?

 

No. I m not sure. But I will check.

 

Is the car working correctly? CEL gone?

 

Does the car have P1000 or P1111?

If P1000 many codes can't flag.

 

I would be willing to bet it's a faulty O2 sensor and you will be seeing the code
P1646 come back after a few drive cycles.