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Thread: REST function problem

  1. #1
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    REST function problem

    another stupid problem... couldn't solve.

    heater control valve and aux pump are all brand new and there is no air in the cooling system.

    rest button usually blows warm air for only 30 seconds and then blows cold air when I normally drive and park somewhere, which means the aux water pump is not working. it does blow warm air though when I connect my car to the battery charger.

    I'm thinking maybe it's a voltage problem? aux pump gets turned off when the voltage is low? but I thought rest function wouldn't work at all if it's the case, am I wrong? (I mean the led wouldn't light up)

    is there any chance some bad relay is causing this?

    ps: outside temp is around 5c. battery shows 12.2v (which is ok under load)
    Last edited by TiesTorN; 01-27-2021 at 01:36 AM.

  2. #2
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    Rest function only works when the engine reaches operating temp and the battery is adequately charged. Have you checked the battery level? Any issues with your alternator or other electronics? It’s also outside temp dependent and only functions below 15 degrees Celsius and when the ignition switch is in the zero or 1 position.
    “She’s the last of the V8’s, she sucks nitro...phase 4 heads, twin overhead cams...600 horsepower through the wheels, she’s meanness put to music...”

  3. #3
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    I'm well aware of the necessary conditions for it to work. that's not what I ask.
    Last edited by TiesTorN; 01-27-2021 at 08:37 AM.

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    Good luck getting help with that great attitude of yours.... TTtwister was only trying to help you, jeez....
    Last edited by BimmrMeUpSnotty; 01-27-2021 at 07:27 AM.
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    well... it may have seemed a bit harsh though it wasn't my intent. I'm just fed up with these intermittent stupid problems that I can't solve and I get angry because of it

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    I had the same reaction as Scotty.....if you are that upset, you might want to take a moment before hitting the "post reply". We are a very giving community here and want to help, but I can assure you that if there is a hint of attitude or rudeness, you will be on your own.
    And, as far as your problem, I would get a scanner, I think the Foxwell does it, that you can activate different modules/items. This would allow you to confirm the operation of you aux. pump.
    Quote Originally Posted by TiesTorN View Post
    well... it may have seemed a bit harsh though it wasn't my intent. I'm just fed up with these intermittent stupid problems that I can't solve and I get angry because of it

  7. #7
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    The aux pump should be relatively easy to diagnose manually. Turn your heat all the way up, center vents on red dots, turn ignition to position 2 and then check radiator overflow bottle for movement (may take a few moments for coolant to circulate). If the aux pump impeller isn’t moving, you can also pull the switch lead at the pump and try to trigger it directly with 12v at the connector. Maybe you got a bum pump out of the box.
    “She’s the last of the V8’s, she sucks nitro...phase 4 heads, twin overhead cams...600 horsepower through the wheels, she’s meanness put to music...”

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    aux pump is working fine, tried it with direct 12v before. and as I wrote in the first post, it works when my car is shut off and connected to a battery charger. weird situation.

    maybe an aged relay thinks my system voltage is too low while using battery and switches the pump off? is it even possible?
    Last edited by TiesTorN; 01-27-2021 at 09:13 AM.

  9. #9
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    No relay, the aux pump is directly powered from the HVAC panel, same for the 2 solenoids above the pump.
    You battery voltage is too low so it shuts the pump off. Put a meter on the battery and watch the voltage drop after you press the REST button.

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    Quote Originally Posted by JimLev View Post
    No relay, the aux pump is directly powered from the HVAC panel, same for the 2 solenoids above the pump.
    You battery voltage is too low so it shuts the pump off. Put a meter on the battery and watch the voltage drop after you press the REST button.
    that's what I think but, shouldn't the rest button led shut off when that happens? everything seems to be in working order (blower fan blowing air, flaps moving inside, led light etc) other than the aux pump.

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    12.2V is very low - I'm surprised you can even start the engine (normally) with that. I think you have to take care of that problem, first, no matter what. And, as others mentioned, this is most likely the reason the REST function isn't working. Charge/load test battery to double check... but chances are you need a new one.

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    I don't actually. it's a 3 year old battery. 12.2v under load cannot be considered as very low.

    I have a smart charger which can measure the capacity. a few months ago I discharged and charged the battery 3 times and looks like it can still hold 60 amps.

    even if it was very low, as I said earlier, it shouldn't have allowed me to turn on the rest function at all, but it does. there is a contradiction.

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    "Under load" sounds like you're saying when "on the throttle"? Some smart chargers aren't all that smart, either. There's too many unknowns there that make it hard for us to know what's going on. But, what does the battery measure right at the battery in terms of voltage? Put a voltmeter meter directly on it and let us know the voltage. Do this... engine off, open the trunk... then turn the lights on for about 5 minutes and honk the horn about 10 times... then let the car sit (still trunk open) for 20 minutes... then measure V at the battery. Report back.

    Contradiction... actually, isn't that how it's supposed to work? Turn it on... the light goes on... the computer evaluates the situation and decides it's a no-go and then turns it off.

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    Well, we all already know that these cars modules get goofy at anything below 12.6v. Plug in your charger and then run the residual heat and see if the pumps activate.
    Set the controls for the heart of the sun

  15. #15
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    MAX button info. (cut and paste)
    Activation criteria continues to be:
    • Ignition “OFF” or in KL R.
    • MAX button pressed.
    • Outside temperature below 60° F.
    • Coolant temperature above 80° C.
    • Battery voltage above 11.4V.

    Don't you have an 88°C t-stat? If so that and your battery could be why it's shutting down earlier than expected.

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    But his little circ pump will run when he activates the "rest" function with a battery charger connected, but will not work without the charger with the engine at the same temp conditions. So, it must be voltage related and a new issue we have not seen yet (or at least I have not seen yet). Likely the HVAC panel has a voltage sensor that is reading incorrectly and it thinks the voltage is below 11.4, but its really not that low. I'm not sure where the HVAC panel gets its voltage info from though. Internally or passed on from one of the other modules.

    Maybe check the high OBC test #9 and see what it says.
    http://mr-fix.info/bmw-e39-obc-hidde...agnostic-mode/

    It may be something there, but the HVAC may have its own voltage sensor, I'm not sure.
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  17. #17
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    Ties needs to monitor the battery voltage with the REST function activated, if it drops like a rock the battery could be on it’s last legs.
    The temp reading should be coming from the dual temp sensor so when the REST function turns itself off he should look at the temp in the cluster, Test 7 to see if it’s above 80ºC.
    At least that will rule out 2 of the variables.

  18. #18
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    I think he said he had 12.2 volts at the battery when trying to run the circ pump (battery under a load), but maybe I misunderstood what was said. And the pump will run when he hooks up the charger, so the temperature from the sensor should meet the needed criteria.
    98 540i 6, 525 whp, 120 mph 1/4, V3 Si S/C'er @16 psi, W/A I/C, Water/Meth, Supersprint Headers, HJS Cats, 3" Custom Exhaust, UUC Twin Disc, Wavetrac LSD, GC Coil Overs, Monoball TA, AEM FP, Aeromotive FPR, AEM Failsafe AFR/Boost, Style 65's w/275's, M5 Steering Box, Eibach Sways, M3 Shifter, Evans Coolant, 85 Deg Stat, PWM Fan, 10" Subs, B.A. speakers, Grom Aux/BT, Still Rolling as my DD!

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    Quote Originally Posted by philly98540 View Post
    I'm not sure where the HVAC panel gets its voltage info from though. Internally or passed on from one of the other modules.

    Maybe check the high OBC test #9 and see what it says.
    http://mr-fix.info/bmw-e39-obc-hidde...agnostic-mode/

    It may be something there, but the HVAC may have its own voltage sensor, I'm not sure.
    The ECU/DME is responsible for monitoring the battery voltage. It passes this information via the D bus to the IKE/cluster which distributes it to related modules including the IHKA over the K bus. So no separate voltage sensor in the HVAC panel. If there’s a problem with the IHKA you should be able to pull fault codes with INPA/Ista as mentioned above.


    According to Rob Siegel, resting battery levels of 12.2v or below are considered very low. Levels under load should be higher with a healthy alternator. I know the DME begins cutting back power to secondary systems/modules in low power conditions, which is why the REST function is triggered below 11.4v and fan speeds can auto decrease.

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  20. #20
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    Quote Originally Posted by JimLev View Post
    Ties needs to monitor the battery voltage with the REST function activated, if it drops like a rock the battery could be on it’s last legs.
    The temp reading should be coming from the dual temp sensor so when the REST function turns itself off he should look at the temp in the cluster, Test 7 to see if it’s above 80ºC.
    At least that will rule out 2 of the variables.
    yep... battery voltage is usually around 12.2v with the rest function enabled. this morning I took my multimeter with me to work and checked it after I parked. it was 12.18v with rest function on, outside temp was 2c and the coolant temp was 93c. I know the voltage is not so good, but it's nowhere near the 11.4v mark where it shuts down.

    aux pump works when I connect my car to the battery charger though.

    maybe my hvac unit is faulty

  21. #21
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    What't the resting voltage of the battery, though (see above).

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    If the REST works fine when connected to your battery charger I say your HVAC panel is good and the battery is the problem.
    How long will the REST function keep the aux pump running for and what is the battery voltage when the aux pump stops running?

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    Quote Originally Posted by DennisG01 View Post
    What't the resting voltage of the battery, though (see above).
    didn't check that, will do asap

    Quote Originally Posted by JimLev View Post
    If the REST works fine when connected to your battery charger I say your HVAC panel is good and the battery is the problem.
    How long will the REST function keep the aux pump running for and what is the battery voltage when the aux pump stops running?
    it never starts running

    I'll need to check it again when I connect it to battery charger to see if it's consistently working when connected. maybe it worked by chance before.

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    With these cars (or any car that is voltage sensitive), it's always best to start with the battery and clean, solid connections. Otherwise, you're running all over the place chasing ghosts. If the battery is on it's last legs (so far, it sounds like that's the case), you might as well replace that anyways before you do anything else.

  25. #25
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    Get it running using the battery charger, then disconnect it and monitor the battery voltage.
    Your pump motor is magnetically coupled to the impeller, no direct connection to the motor armature. You could have something inside the pump interfering with the impeller.

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