Air Conditioning not working - fault codes inside

[z4_spiral]

Ok, here's the first (of probably many) threads about various problems I have with the car. This one I knew before I bought it - the AC does not work. I've taken it for a regas, but alas still nothing.

I'm a curious fellow though, so I aquired a copy of ISTA and have 3 IHKA errors in it (more as well, but not related to IHKA):

000006 IHKA: Supply, pressure sensor AUC
000008 IHKA: Pressure sensor
00000F IHKA: AUC sensor

I would be amazed if these aren't related to a single fault somewhere. Ista's test plan only has steps to look at the first error, the supply, which kind of makes sense if it can't see the supply, can it? It wants a voltage measurement that requires removal of the IHKA module (A11, that right?) and somehow getting a probe in there when I assume the car is on - see end of post.

I've loaded INPA as well, and confirmed the pressure sensor is reading 0bar/0.1V, and the AUC sensor is reading 0.1V too. I would _suspect_ the same 5V source is used for both, though they are separate pin outs on the IHKA module.

Before I go dissassembling the car, has anyone else had these symptoms and can offer some alternate debugging steps? Or even had similar symptoms and found a root cause? Perhaps a common point in the loom/ground that fails? I was thinking of the following:

* Testing the pressure sensor: Apply 5V myself and check the voltage of the sense pin, validate that works.
* Just unplugging the AUC sensor, and see if that makes things work
* Unplug the pressure sensor, and see if that makes the AUC sensor work
* Re-do my awful attempt at faking the pressure sensor signal with a home made voltage divider (2 1M resistors with a sense pin in the middle, should give me 2.5V if the supply is right, but it was dark outside so I'm going to try this tomorrow).


ISTA test steps. Terminal 31 I've learned is the generic code used for a ground, which makes sense if testing the supply, but I've no idea how to be at this with the supply on? Tips on testing this would be greatly appreciated.

Voltage measurement
Test probe 1 (+):
Automatic air recirculation control+ automatic air recirculation control voltage supply
Test probe 1 (-):
31L Terminal 31, earth connection
Measure at:
A11 Control unit for heating and air conditioning system
Specified value: 4.5 ...5.5 V

 

[rocket70]

Sounds like the system is short of refrigerant. Being an ac guy... i would start by putting my gauges on and running the system.

 

[rocket70]

Sorry just read the post in properly and you've had a regas. Did it work at all after the regas?

I remember doing a regas on a Merc and the guy had to take it to merc to get it reset before it would run.

 

[enuff_zed]

Back right corner of the engine bay, beside the regas point is the sensor. If it fails it won’t signal the compressor to run. Cheap and easy to fit a new one but you will lose gas no matter how quick you are. Be sure to hold the pipe with a wrench too as it is screwed in tight and will easily twist the pipe.
Wife’s car had exactly this problem. Ten minute job then regas again.

 

[z4_spiral]

Thanks for all the quick responses! Yes I've had a regas, first thing I tried thinking "ah this one will be easy won't it". Spoiler, like everything with this car so far, it wasn't. At this point though, I don't think it the regas actually matters, because the system thinks there is 0 bar in there, so deffo looking at a sensor/electrical problem imo - would be reading ~1 bar if it was a leak to atmosphere, aye?

I need to get that sensor either confirmed dead or reading correctly first. I'm going to go out and unplug both AUC and pressure sensor later today (I've read one instance where a bad AUC sensor caused a fault with the pressure one), and measure the sense supply voltage to ground at the supply voltage (. If that's 0, then I think I have to assume the sensor is good (for now) and diagnose that first. I don't have good tiny probes for my multimeter (I usually do guitar pedals, nice and chunky components), so will stick a wire in each and see!

I should also confirm the sensor function by applying 5V myself. No good clips for it, or a 5V supply handy, so going to rig some batteries together to get 4.8V (should be close enough, I believe ISTA says the supply can be 4.5V-5.5V), and see what the sense pin says. Might not have time for a few days though, busy being back to work :'(

For reference, I looked up the wiring diagram for the pinout:

IHKA Pin (large plug) - purpose - pressure sensor pin
pin 16 supply 5V pin 3
pin 17 sense (0.4-4.6V healthy) pin 2
pin 18 ground/termial 17 pin 1

 

[enuff_zed]

The sensor is pretty cheap. Could just swap in a new one?
This is the one I got: https://www.ebay.co.uk/itm/125655469538

 

[colb]

The AUC sensor is clipped at the top of the radiator under the front plastic cover, its also refered to as a stink sensor as it sniffs traffic fumes from outside the vehicle and will control the fresh air intake on the aircon system. If it detects traffic fumes it closes the fresh air intake to stop the fumes entering the car. Last time I looked it was about £70 from BMW. You can buy the actual componant that is inside the sensor from an electronics company for around £17. I did this but it still throws a code and I now ignore it, it has no affect on the rest of the aircon system working. If the blower motor stops working its usually down to the car having entered into Transport mode which is caused by low battery voltage being detected and the car closes down some of the systems in order to conserve power for starting. Usual systems that get closed down are Aircon and heated rear screen. Transport mode has to be reset using diagnostic software, BMW Scanner 1.4 has the ability to reset it. Transport mode should have been deleted by the dealer when the car was sold new when it had its PDI, most did not carry this out, maybe because it was expected that the car would be returned to them should it go into transport mode so they could charge for resetting it?

 

[Pondrew]

Cheap and easy to fit a new one but you will lose gas no matter how quick you are.

It is against the law to deliberately or knowingly release refrigerant to the atmosphere.
Just saying s'all!

 

[enuff_zed]

Cheap and easy to fit a new one but you will lose gas no matter how quick you are.

It is against the law to deliberately or knowingly release refrigerant to the atmosphere.
Just saying s'all!

Well I didn't know it would happen until it was too late. :wink:

 

[Pondrew]

Well I didn't know it would happen until it was too late.

As I make a living out of this shite, if I used that defence I could still be imprisoned for up to 5 years!! :x

 

[enuff_zed]

Well I didn't know it would happen until it was too late.

As I make a living out of this shite, if I used that defence I could still be imprisoned for up to 5 years!! :x

Well in that case I'll just them you did it for me. Hopefully we can keep in touch? Think most prisons have wifi?

 

[Pondrew]

Well in that case I'll just them you did it for me. Hopefully we can keep in touch? Think most prisons have wifi?

I wouldn't do well in clink mate. I'm too pretty! :lol:

 

[z4_spiral]

I wouldn't do well in clink mate. I'm too pretty! :lol:

@colb I saw your write up on that before, I was actually planning on doing that if indeed my AUC sensor is condirmed bad, it was an excellent writeup. Think I can test that in the same way as the pressure sensor, but at least I can take it into the house where it isn't minus baltic degrees. Now that one I expect to be broken. As I'm testing functionality I don't *think* I need the heater element working, should be able to supply 5V/Ground then check the sense to ground on it. One for after this meeting perhaps...

Blower works fine, as does the defroster after I fixed the roof wiring, so don't suspect transport mode.

 

[z4_spiral]

Just to accompany my claims about the sensor voltage readings, I present some INPA screenshots - see the pressure/auc voltage (and thus, the actual pressure reading)? Primary suspect.

 

[z4_spiral]

Well I nipped out there to do a quick test - went and unplugged both sensors and checked the supply/ground voltage. 0V for both, so regardless of the sensors working or not, there's a problem with the supply. ISTA says to check the supply at the rear of the IHKA module, which makes sense as that will tell me if it's a module or a wiring problem (not sure what's worse) so when I get an evening I'm going to try and get it out and see if there's anywhere I can get a probe in there. Not sure how to probe something when it needs to be plugged in to be turned on without removing a pin, which I don't have tools to do but getting it out will hopefully reveal it's secrets.

I imaging at the end of this I'm going to replace the sensor anyway :roll:

 

[z4_spiral]

Ok, tested the wiring loom this morning from the back of the control module. Continuity was good. Then rigged up a 5V supply (don't ask how) over the loom to check the sensor values - returning 0.7V, which is in spec (though don't know what that translates to) and more than the 0/0.1 that the module knows about.

So I think the module is toast and there's an issue with the 5V supply, but I could confirm that by sending a signal back along the sensor when it's plugged in. 1.2V from an AA should do it... :lol: If the car sees that, then I'm almost certain it's the module. Though to be fair I've never diagnosed anything that's not a guitar pedal before, and these are way more complicated so I hope I'm wrong. Probably take it to a dealer to confirm, shouldn't take long to confirm the module according to ISTA.

 

[enuff_zed]

Ahem................
https://z4-forum.com/forum/viewtopic.php?t=138297
Just saying. :wink:

 

[z4_spiral]

Of course, I refitted the thing this morning after checking didn’t I? Will pull it later and check part numbers, then probably take it :roll:

 

[enuff_zed]

Of course, I refitted the thing this morning after checking didn’t I? Will pull it later and check part numbers, then probably take it :roll:

No worries, just me being cheeky and opportunistic.

I also have a pressure switch which I'd chuck in with it if that helps?

 

[z4_spiral]

I appreciate the cheek here honestly, £20 for a confirmed working unit and a pressure sensor? Unreal. Well, that's a LOT faster to pull out when you've already left the vents out and actually know what you're doing! I've attached an image below, should be compatible... right?

I've heard rumors that older IHKA's don't need programmed. I'm not sure if I believe that (because bmw things), any insight on that? If you've done coding before, any chance you could code the vin in before sending it, assuming it's compatible ok, or is that something that needs to be in the car?