P38A Rear screen heater

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Sonnycbr

Active Member
Posts
131
Location
Sunderland
Hello again folks, my latest headache is that the rear screen heater is on permanently. I have no idea how long it's been like that but I need to fix it. Where do I start? What could make it stick on? The switch lights are not on for either screen heater so it could well be the case that both heaters are on permanently. Do they share a fuse? If so what number is it? Tia.
 
The button has 2 bulbs, one for illumination and one for on/off status. They are make/break switches to send a signal to the ecu, so they should turn off and stay off with the ignition.
I'd start by swapping the relay
 
kermit_rr said:
The button has 2 bulbs, one for illumination and one for on/off status. They are make/break switches to send a signal to the ecu, so they should turn off and stay off with the ignition.
I'd start by swapping the relay
Click to expand...
Cheers Kermit, I'll do just that. However, here is where I really show my ignorance of all things electrical. Where are the relays housed, and how do I know which one to change?
 
kermit_rr said:
They are next to the battery, there's a sticker on the lid to say which is which
Click to expand...
Had a look and sure enough they're exactly where you said they'd be. I took Nos 4 and 5 out and give them a good looking at. Not knowing what they are or what they do was a slight impediment to my inspection. I'll order 2 new ones and, fingers crossed my problems are all behind me.;)
 
Sonnycbr said:
Had a look and sure enough they're exactly where you said they'd be. I took Nos 4 and 5 out and give them a good looking at. Not knowing what they are or what they do was a slight impediment to my inspection. I'll order 2 new ones and, fingers crossed my problems are all behind me.;)
Click to expand...
Before you order new relays, you can use a relay of the same colour from another position and see if that fixes the problem.
It seems unlikely that 2 relays would fail at the same time.
 
Here's what's happened today: took the battery off charge this morning and checked voltage, it started at 14.7 but dropped rapidly to 9.5, just started the engine. Did a bit shopping, drove the car about 3 miles and checked voltage when I got back. It started off at 10.4 but it was dropping slowly as I watched it. I then took both screen heater relays out and replaced them with two relays same colour. I then took car out again, did about 3 miles again and checked battery when I got back, same as before, started off at around 10.8V but slowly dropped as I watched it. I won't even begin to guess what all this means.....over to you guys.
 
Sonnycbr said:
Here's what's happened today: took the battery off charge this morning and checked voltage, it started at 14.7 but dropped rapidly to 9.5, just started the engine. Did a bit shopping, drove the car about 3 miles and checked voltage when I got back. It started off at 10.4 but it was dropping slowly as I watched it. I then took both screen heater relays out and replaced them with two relays same colour. I then took car out again, did about 3 miles again and checked battery when I got back, same as before, started off at around 10.8V but slowly dropped as I watched it. I won't even begin to guess what all this means.....over to you guys.
Click to expand...

Take all readings with engine off.

1) charge it with battery leads disconnected and leave it 24 hours and see how much the voltage drops.

2) charge it but this time remove those 2 relays before reconnecting the relays and then see where you are 24 hours later.

3) charge it but this time leave the 2 relays in for 24 hours and then see what the voktage is 24 hours later.

Eric does a good video on YouTube on how to chase battery drain issues. I use junp leads so I can shut the bonnet but you can wedge the bonnet switches open if you want to leave it open while you wait for it to go to sleep.
 
Sonnycbr said:
Here's what's happened today: took the battery off charge this morning and checked voltage, it started at 14.7 but dropped rapidly to 9.5, just started the engine. Did a bit shopping, drove the car about 3 miles and checked voltage when I got back. It started off at 10.4 but it was dropping slowly as I watched it. I then took both screen heater relays out and replaced them with two relays same colour. I then took car out again, did about 3 miles again and checked battery when I got back, same as before, started off at around 10.8V but slowly dropped as I watched it. I won't even begin to guess what all this means.....over to you guys.
Click to expand...
If those voltage readings are correct, the battery is knackered.
 
Grrrrrr said:
Take all readings with engine off.

1) charge it with battery leads disconnected and leave it 24 hours and see how much the voltage drops.

2) charge it but this time remove those 2 relays before reconnecting the relays and then see where you are 24 hours later.

3) charge it but this time leave the 2 relays in for 24 hours and then see what the voktage is 24 hours later.

Eric does a good video on YouTube on how to chase battery drain issues. I use junp leads so I can shut the bonnet but you can wedge the bonnet switches open if you want to leave it open while you wait for it to go to sleep.
Click to expand...
That's my weekend project. I'll take notes and post the results asap. Any idea of the title of Erics video? Thanks for the help.
 
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