Took this 2008 Jaguar XJR in for a smog check about a week ago and the smog technician showed me that there was a "pending" p0128 code flagging "Coolant thermostat (Coolant Temp Below Thermostat Regulating Temperature)". No check engine light was illuminated on the car at this time.

A few days later, I'm driving up a steep hill and get the "Restricted performance" light on my dash followed by limited power and a check engine light and just 1 code, P2601 (Coolant Pump Control Circuit Range/Performance).

After doing some research on the forums I found a few people saying that the P2601 code can show up indicating a faulty supercharger pump which is completely different than the coolant auxiliary pump.

I understand the supercharger pump is a $700 part, the coolant auxiliary pump $100, and thermostat just $17 so what I'm wondering is if someone can tell me if the pending thermostat related code of p0128 I had could be related to this incident and that this might all just be due to a bad thermostat? Or would a P2601 code be totally unrelated and must be either the auxiliary pump or super charger pump? Going to change the thermostat anyway since it's so cheap and inspect all the hoses while I'm at it since I just got the car but wondering if I should also swap out the $100 coolant auxiliary pump at the same time or just thermostat first and test?

Lastly, any idea how easy these two pumps are to get at? Will they need to be accessed from the bottom? With car on ramps/jacked up?

 

Can't help with the codes but have some info on the coolant pumps having just replaced my supercharger coolant pump;
I have 79k on my xjr and the coolant pump runs all the time with the ignition on. I started hearing a horrible screechy rough noise from the front of the engine with just the ignition on. Was removing the front bumper to do other things and tracked this horrible noise to the supercharger pump on its way out, which at my millage seemed not unusual from reading posts on the issue.
The original Hella part is expensive, around 400 Euro in my neck of the woods but nobody fits this from what I can gather. Everybody goes for a Bosch alternative, also fitted as oem to Mercs which only costs around 100 Euro. Google 'jaguar xjr supercharger pump Bosch'
The Bosch unit is slightly bigger but will go in the original spot with a a small alteration to the the bracket and you need to add/change the electrical plug (The Bosch needs an EV001 type I think, its the kind used for injectors).
To get at it front undertray off, and front bumper cover off, its located at the bottom and left (looking at the front of the car) of the main rad behind the bumper front member. Pull off the the bottom hose from the supercharger radiator, drain the coolant and you'll be able to the old pump out downwards by wiggling it around a bit past things. As I said Bosch unit is slightly bigger so is a bit fiddly to get back in the same space but its very doable. The advice I read was to replace the original hose clips with jubilee type so I did that.
Fill back up the coolant.

On the auxiliary heater pump I haven't done this yet but its located down below the coolant expansion tank on the left (looking at the front of the car) behind the main radiator. People have rebushed this pump rather than replace it. Again it seems that this runs all the time and does just wear out and needs refurb/replacement.

 

Thanks Paddy... very helpful tips. Sounds like the Bosch pump is the way to go although I'm not getting that screeching sound. Were you not getting any codes flagging? Just the noise which you traced to that pump?

I've never had to re-wire anything electrically but I suppose once I get the right connector that fits the bosch pump I just cut the pre-existing connector off then splice the wire to connect the proper connector and finish with electrical tape? Seems easy enough if that is all that it entails, I'd just hate to get this all disassembled then run into a problem I can't figure out.

Found a good link explaining swapping out the S/C pump for anyone else planning the same job... https://jec.org.uk/forums/viewtopic.php?t=10098

Any insight on the codes would be greatly appreciated, while I'm in the area are there any parts I might as well replace once I've got the bumper off? The car has 83k miles so will inspect all the hoses for wear but if any parts that are known to fail in the general area I'll be working on I'd be happy to replace as preventative maintenance, any guidance there appreciated.

Mahalo

 

No I had no codes, just a horrible noise.
In terms of the connector I just soldered the new one onto the existing lead after checking which was +ve and which was -ve from the electrical wiring diagram and checking with a meter with the ignition on. I would solder or crimp any joints and finish with shrink wrap rather than use electrical tape. This is right at the front of the car so will get all the weather thrown at it.
Modifying the pump bracket just involved bending it and using a longer bolt. The original rubber around the original pump can't be reused as the new pump has a bigger diameter. I used a bit of old door seal rubber instead.
When I had the bumper off I replaced a headlamp washer jet that was duff and all the washer pipework which was cracked and leaking, removed the headlamps and installed new earth points behind each headlight, and replaced a couple of the parking sensors and cleaned up all the electrical connectors.

 

It's quite simple really: when these cats are parked for a long time, they suffer from the following causes, each one of which, on their own, result in Restricted Performance

1. (X308 specific) Bulk Head Connector contacts: these will build up salt residues due to dampness and the difference in material on mating male/female pins (one side is gold-plated, the other is tin). Your knock, crank and cam position sensors terminate here, amongst other vital engine management looms. Remedy: unscrew the centre bolt holding both halves together, clean the male side of the connector (half with pins) with contact cleaner; soak the female half (one with holes) with contact clener and brush out residue with a hard brush. Wipe with a lint-free cloth and screw back together. I would start with this course of action before anything else down the list. This is 50% of your failure causes.
2. Knock Sensors: these suffer from build up of layers of oxide and/or salniation underneath the face of the connector. Remedy: unbolt both sensors, take them out, clean the underside of both connectors to a shine, and the mating serface on the engine block likewise. Also check the econoseal connectors at the end of the sensor cable, and likewise the mating female connector on the engine block - clean these to a shine with contact cleaner, wipe and install. This is some 30 - 40 % of the cause
3. Paddle and Throttle Position sensors: these are two potetiometers mounted on the throttle body. Over time, they either go out of alingment (one is adjustable via two slotted screws) or simply fail and need to be replaced. In about 5% of cases, this will cause restricted performance. In remaining cases, engine failsafe will ensue. Remedy: Where a restricted performance message is displayed, you can probably get away with cleaning these sensors if you're capable of electronic component repairs. Where an engine failsafe message is displaed, then turning the ignition to position II (on), and adjusting the sensor with the two slotted screws until the restricted message disappears is the way to do it. If you're realy unfortunate, then you'll have to replace the throttle body altogether, which is not all doom and gloom - several outfits will sell you a reconditioned.
4. Coil Packs: like any electrical component, these have an operating life, and 20 years later, you can't expect them to all be healthy and go forever. When you have repeated and/or multiple cilyndar misfires, then your cat will go restricted performance. You don't always get a fault cause, particularly if it's intermittent; the cause is the way the ECU algorithms work, which I have neither desire nor breath to go through. Remedy: if you're lucky, then misfire would have triggered a fault code to tell you which cilyndar this is taking place at; now some would say change that coil, which would probably suffice; but if you consider that all these coils are likely to be originals when the cat left her den, then they're all on the way, so I would replace all of them as a set. Originals are Denso, and Denso stoped making these. Lucas replacements are bound, reliable and just over £30 inclusive of the gove's Vodca and Tonic, if you know where to buy.
5. Fuel pumps: these are a bit contravercial; when they fail, the cat would start - full stop; and it is a common fault with not only the Jag, but just about any other car - they will cease, particularly when they've not been turning for a while. That said, sometimes pressure goes low due to partial failures at load, or worse, they stop and start mid-cycle. Remedy is trivial; on the XJ-R, I'd replace both and not just the failed pump.

As a matter of record, I have come across all of these symptoms over the years, and continue to do so.

Hope this helps ..

 

I have a knock sensor code and LP on the read out. May I ask where this connection is located? Thanks