Hi guys , I've looked at the relevant threads, but haven't found anything that fits my problem. Car is a 2003 XK8 4.2 Convertible.

We spent a few days in England, where you need to use the windshield washer system from time to time. The wipers work, but the pump doesn't, so no water gets onto the windshield.

The pump runs when 12 V is applied directly. However, no current is present at the yellow/green cable on the pump connector (measured against ground) when the button at the stalk is pressed.

I initially suspected the wish/wash stalk switch, so I checked the signal (ground) from the stalk at the input of the BPM (FC14-37, green/red), and it is present when the button is pressed. However, the output signal (12V+) to the pump (FC14-26, yellow/green) is missing.

I would conclude that the BPM has a fault, but I can't really believe that because there are no other symptoms. Given the multitude of functions controlled by the BPM, that would be unusual.

Has anyone ever had a failure like this, or have I perhaps overlooked something?

Thank you for your advice.

Fritz

 

With the wipers off, if you press the screen wash button on the stalk, do the wipers run for a short period? That will prove if the button is working as intended.

Check all your fuses to the BPM and read this thread where a similar symptom lead to replacing the BPM, but it turned out it was a blown fuse:-

https://www.jaguarforums.com/forum/x...cedure-292119/

 

Yes, that's a good point, thank you. The BPM has three Battery+ supplies, and I will check all the fuses.

I will also try to connect a direct ground to the input pin at the BPM. It may be that the ground from the wipe switch is present but insufficient and therefore not being processed. Initially, I only measured continuity, not resistance or voltage drop.

Fritz

 

Do the wipers run when the washer button is pressed? If so you can rule out the button.

If all your fuses check out, I think I would just wire the pump direct from the button via a relay. If your car has the power headlight wash (or at least the wiring) I would re-purpose that. I disabled the headlight washer on mine as it just sprays the (freshly washed) bonnet with windscreen cleaner - the wiring, the relay and the fuse are all sitting there ready to be repurposed on mine. I've never liked the fact that the BPM is directly driving a fairly high current device.

 

The wipers always worked when I pressed the wipe/wash switch, but the pump didn't. It indeed stands to reason that the button must be o.k then.

My car comes without headlight cleaning system, and that fine with me, the power wash feature is mostly annoying.

In fact, I found today that fuse #7 on the driver's side has blown. With a new fuse, the pump works, of course. Thanks again for the tip, I don't know when I would have figured that out.

I'll keep an eye on it now and use the washer system more often. If the fuse blows again, I'll also install a relay in between.

Thanks, Fritz

 

103s are known for losing BPM outputs but never heard of a washer pump being one of them

 

Well done for finding the problem. Just goes to show, always start your fault finding as if you are working on a 1970s British sports car and check the fuses, the relays and the wiring before moving on to the electronics.

It was @michaelh who identified the suspect fuses on the other thread - interesting that is two fuses going like that. I guess the windscreen washer pump starts drawing more current as it gets older, especially if it gets jammed. Luckily the fuse protects the BPM circuitry, but a relay would be a worthwhile bit of extra protection.

 

What irritated me was that 95% of the BMP's functions were fine. Also, it was no longer on my radar that the BPM has three Bat+ inputs.
Otherwise, if a control unit is suspected of failing, I first check the voltage supply.

Fritz

 

Ho hum. I missed one additional (20A) B+ feed to the BPM although, unlike the other three, it is not explicitly marked as such in the EGs for either 4.0L or 4.2L. It appears to be related to the steering column motors.

So several separate fused circuits. Unfortunately not always sufficient to protect the BPM, hence my link to K. Westra's thread. Thankfully, the emission of magic smoke appears to be confined to earlier convertible cars that have had work done on the header rail.

 

Hello colleagues, I regret to inform you that my good friend Fritz ("flatsix") passed away unexpectedly last week from a severe heart attack - shortly after this post and his trip to England together with his wife and his XK8. He was also a member of the local Jaguar community here in the area as well as a very active part of the biggest german jaguar forum, being extremely knowledgeable about all technical things related to our Jaguars. He was always the right man to offer us advice, support and famous for his subtle humor. We are very saddened by his passing.

Best regards, Bernd

 

Very sorry to hear that news. Condolences to his friends and family.

 

Condolences to all....