I have a 1995 xjs Convertible. LHD.
Occasionally the engine air compressor (Emission control) comes on after the engine is turned off and drains the battery. Is there a relay that controls this??

 

Are you sure it's the air pump thats coming on and not the electric fan ? The airpump is mechanically driven off the crankshaft, so I think it's impossible for it to run without the engine running, and also it's not electrically powered.

The fan will sometimes "run on" after the engine has been shut off, but it is controlled by a thermostat and should go off after a few minutes, so it should never flatten the battery. First confirm whether it's the electric fan thats running, then we can help you troubleshoot whats wrong with it

Is this a 6.0 V12 or a 4.0 I6 ?

Put your car details in your signature, then we don't have to keep asking

 

Yes it is the air compressor pump. It is a 4.0, I6 cylinder. The pump is electric. I have it unplugged at the moment and this causes the Check Engine light to illumminate. Something is turning it on occassionally when the engine is off.

 

@olsthro

Wow, ok, I stand corrected. I had a look at the circuit diagram and the air pump is driven by a relay that is connected to 12V battery power (not ignition power) so in theory, if that relay is failing and closing when it shouldn't, your air pump could start running when the car is turned off.

This relay is on the left hand side component panel under the hood, at the back of the panel on a green base. I would start by inspecting and/or replacing this relay first. If it's not that, I would inspect the wiring loom from the ECU because the pump is activated by grounding the output, so if you have a short somewhere, this could also start the pump running, although it would seem strange that this short is happening when the car is completely still ? (Usually intermittent shorts happen when the car is moving and something jostles against something else)

 

Thanks so much. I will try and locate this relay, replace it and see if that is the solution.

 

I can;tseem to fnd the relay you referred to. I don't see any on the left side that have a green base. They mostly are all blue bases.
R