1991 XJ40 heater & non start


I have two present problems with my XJ40, 1991 3.2 litre

  1. The heater system (has air con). all the blower positions worked fine till a week or so ago. Now just the full blow inc demist/defrost, and full blow work. No medium or slow.

  2. When warm/hot, and turn eng off, it wont restart on first turn over. It turns over several times, but no start, however, if I switch off, then switch on and start, it fires immediately. I have seen on the fault prog FUEL…

Anyone advise please>?

Thank you. Neil

Hi Neil, it sounds like the speed control circuits in the blower motors have failed. They all do sooner or later! If you search “Darlington transistor” in the XJ40 archive, you can read how to fix the problem. It’s unusual for both to go at once so probably one has been gone for some time and now both have.

The engine issue sounds like the non-return valve in the fuel system has failed. Again a search for “fuel non-return” will probably lead you in the right direction.

Welcome to XJ40 ownership!

Neil …

Both blower assemblies (the car has two) have to be operating to get proper airflow out of the system. The two assemblies blow air directly across toward each other where the air then meets in the middle and is forced up into the the box that houses the evaporator, heater matrix, and two blend “doors” rollers.

Since there is no “one way” door on the assemblies (a modification that some people make) if one fan fails the operating fan simply blows it’s air across into the failed unit and not up into the box. Because of this poor design if one fan fails you don’t get 50% airflow, you actually get very little.

To troubleshoot this you should first pull the left fan assembly fuse and listen to the sound of the fan and feel the airflow. Then do the same with the right assembly fuse. If only one has failed you’ll know it.

The only way both fans would completely stop working at the same time would be a problem with the fan controller in the ski slope, but since you have high speed that’s not the case. As Larry very wisely pointed out it’s highly likely that the Darrlington transistor in one or both of your units has failed ,…, a VERY common failure and sadly not an easy fix because the fan assemblie(s) have to be removed to replace the transistor.

Thank you Larry & abercanadian, I will check on the things you mentioned.
Re the heater, is there a “reastat” on the main control panel (with the blower switch & heat control etc) which could be the problem before looking at the actual blowers?
Also, the fuel, I understand what you are saying, but the in tank fuel pump was renewed less than a year ago, and the car starts ok from cold. It only plays up once the engine has warmed.


Simply put, no. The speed is controlled by the circuitry inside the blower housing. If you have high speed only, this is a common symptom of failing darlingtons. I don’t know any owner who hasn’t had to replace those after all this time. I certainly had to, more than once.
You should also take Grooveman’s advice and make check that both fans are operational.
Removing the blowers requires a little bit of contortion as they are held in place by two bolts at the underside of the dashboard. You have to remove the knee bolsters and assorted relays etc and lie on your back with a long-ish extension and socket to remove the nuts on the driver’s side and on the passenger side I believe the glove box has to be taken out also. I have a 94 model which has a passenger airbag so the operation on the passenger side is slightly different.

As far as I know, (I haven’t personally had the issue) you can try repeatedly cycling the ign switch for a few seconds each time before a hot start, so that the fuel pump builds up pressure in the fuel rail. If the hot start is then OK, there’s a pretty good chance the non-return valve is the issue. A way some members have overcome the problem is to fit an additional valve in the engine compartment section of the fuel return line.

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I’m in the middle of this same task, illustrated by this picture of the passenger side of my RHD.

I have a question about replacing the relays. I ordered Hella replacements which turn out to be branded Mahle made in India. Is this to be expected these days?

It is; nobody makes stuff these days, it’s all rebranded production from far away. You usually get the same car part from several different manufacturers and who knows who made it. It is the best you can get though if both mahle and hella put their names on it.

Hi. Well this is odd. Was parked today with eng off but ign sw to power radio, but then, the slow blowers started working! Worked ok all the way home too. So from fast blow only,. all speeds working now! Any ideas please?


Odd indeed! If they work, that does mean the transistors are ok.

There are two relays involved too, you can see the type in dr_gaz’s post just above. Possible that one or both are defective or dirty?

Generally though, these types of intermittent operation quirks tend to be connection issues, so it may indeed stem from the connection at the panel - but take this with a pinch of salt as I have no experience with the panel failing in a 94.
Most electrical climate control problems on my car were either the speed control circuitry in the blowers or cracked joints in the footwell fuse boxes, however cracked joint symptoms affect ALL blower operation, not just the low speeds. No high speed either.

There are some issues with earlier panels as I recall, they involve a micro switch failing …but again, I believe that affected the entire operation of the control panel, not just the low speed.

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Many thanks for your help chaps.



Gentleman …

The left and right blower motors are independently powered through fuses in the left and right footwell fuse panels. So if BOTH fans fail to operate at the same time the odds are 99% (see how cleverly I hedge my bet :smiley:) it’s a problem with the control panel. And if the control pane fails to light up it’s almost always due to a faulty micro switch inside the panel (super easy fix).

If only ONE unit fails to operate at ANY speed it’s a power problem, so start troubleshooting at the fuse panel. If however the blower doesn’t operate at every speed (usually only on high) then there’s a 99.5% chance it’s the internal circuitry in the blower assembly. And a 99.6% chance it’s the Darlington transistor that’s the problem. Oh so easy to fix but a devil to get to.

As far as the relays inside fan assemblies believe it or not you can replace them without removing the assemblies by very carefully reaching in and down through the vent door. It takes a bit of doing but it can be done.