Range Rover p38 hvac problem

**BeianM** · 16th December, 2010, 01:52 AM

Hvac display is not lit, no cig lighter & radio. Circuit diagram shows feed from fuse 8 of the becm. There is power here. Pulling this fuse does not show "fuse 8 failed" message on dash. Pulling out relays 6 & 7 does give this message. At relays 6 & 7 there appears to be no earth & the feed to the circuit has 12v As well as the relay feeds. So appears as if volts coming back from the dead circuit. I can get the unit to operate by giving it 12v at the cig lighter. I have replaced the fusebox.
Your thoughts appreciated

**Meat-Head** · 17th December, 2010, 08:03 PM

that would suggest manky smelly plug full of pig piss.

run new wire from faglighter to that fuse and ~~~~ it off.

suspect loom under carpet rotten as a peach.

**BeianM** · 17th December, 2010, 09:25 PM

Originally Posted by Meat-Head

that would suggest manky smelly plug full of pig piss.

run new wire from faglighter to that fuse and ~~~~ it off.

suspect loom under carpet rotten as a peach.

Nice to hear from you meaty, Yes going to have the seat / carpet out. May need to stitch in an alternative relay up under the dash.
I thought someone would have commented on this before now, looks like dk is short of Range Rover bods.

**Meat-Head** · 17th December, 2010, 09:32 PM

Originally Posted by BeianM

, looks like dk is short of Range Rover bods.

no nobody likes them *THINK* Search by google for p38.com or p38-sad-bastard-.com or something - word on street.

Why ~~~~ around with it, the owner will be

1) Smelly farmer
2) T**ser in a suit
3) Some thug with him name tattoed on his arm, so he knws who he is.
4) Thick smelly horse rider that uses it for towing horse box.

If the customer pisses you off, then assuming it is an auto, SUPER GLUE a 10 amp fuse -top right - in fuse box - under seat - then snigger when the phone rings next.

**BeianM** · 23rd December, 2010, 01:29 AM

Getting there. Looks like the becm has a circuit fault, so have found an alternative circuit to tap from. However still unable to get the blower fans to operate!

**BeianM** · 17th January, 2011, 12:52 AM

Update.
Becm fault, no power from relay 7. this does several circuits. This car had no power to the hevac display, no blower fans working even if i fed 12v to the circuit that lit the hevac & powered the cig lighter & radio. It would also keep the heated front screen on + other stuff that drained the battery.
I got a second hand becm, swapped out the lower board with the original so the car kept its immo & ecu info. Fitted it & all was ok. Hevac worked ok including the fans & no battery drain. However this board was not fully populated with relays so some circuits did not work & failed fuses were reported. I went back to the original board & removed the relay & tested it. It worked ok, traced the circuit to a shorted diode

Replaced said diode & refitted, all is now well so very happy

Just have to fit a new ambient sensor (says temp is 50c) & check why the brake pump is running all the time (hope its just a relay) & I can get shot of the car. Who would have a p38!!

**Meat-Head** · 17th January, 2011, 02:20 PM

!) Can you bump my tips and tricks thread with that about the diode - thanks
2) You you take a photo of said diode and upload - thanks

Meat.

**BeianM** · 18th January, 2011, 10:33 AM

If anyone can help me unlock the spare becm I now have I would be very happy to hear from you.

**BeianM** · 19th January, 2011, 08:29 PM

Another problem, the ambient temperature was reporting 50c !! I removed the sensor & the temp slowly reduced & stopped at -40c. Fitted replacement & still sat at -40c. Tried another hevac controller & this works ok so no wiring fault. Any ideas on how to trigger the hevac back to life? I did read somewhere that some of these have a software fault & do not read for around 15mins. Have left it on for this period but still no go.

Answer:
Looks like this has had a replacement hevac control as the later ones have different software. Land Rover very kindly wrote a bug into it that means the air temp is not updated until the car is travelling at over 15mph (25km/h) Says "therefore will not automatically correct temperature readings when a faulty sensor is renewed" Thanks Land Rover!!

early cars the sensor is in the air duct left side near the filter. Access from inside the vehicle
later cars fit it in front of the left hand radiator.

-10c = 54.3k ohms
0c = 32.1k
10c = 19.7k
20c = 12.5k
30c = 8.1k
40c = 5.4k