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I'm giving you all the cliff notes version of this one. Had a head sratcher today. 2014 Nissan Altima, customer complaint was poor heat.
I confirmed this, not much at idle. Coolant full, no air in it. They had done a lot of stuff to the car already including a new t-stat. I took it for a test ride, lots of heat running down the road. Not so much at idle. I was using a scan tool to monitor the ECT.
Get back to the shop and the heat stinks at idle. Get out the ol' IR gun and shoot the housing with the ECT in it. It read 170. ECT on scan tool reads 216. WTF? Cooling fans blowing their brains out. Air is cool behind the radiator, huh? Lower hose to t-stat is around 110. Uhh....what?
Thermistor circuit right? ECT? Two wires, pretty simple. Usually.
KOER, unplugged I got 4.77V on signal wire and .01V on ground. OK, that ground seems good 4.77V is odd for a unplugged thermister. I am expecting around 5. Service manual even states approx. 5V. Check a few other 5V ref sensors and all read 5V, including the IAT. So the wiring checked out and I have 4.77V at the ECM. Checked ECM power and grounds=all OK. So I'm about to call a ECM on this thing. I think we'll check another Altima if we have one. We happen to have a 2013 Altima, 4.77V on the signal wire unplugged at the ECT is NORMAL!!!! WTF, Nissan. I've never seen this nor been told this EVER. So needless to say we have problem here. I THINK its a skewed sensor, but I won't be able to confirm because I got the car hot and the customer was waiting. So I'd need it overnight to see how it compares to IAT, Oil Temp, etc...at cold temp.
So am I just stupid or is 4.77V NOT approx. 5V on a COMPUTER SIGNAL CIRCUIT!!! Last I checked 0.1V of voltage drop is generally accepted for a wire. We are dealing with a SENSOR!!! IMHO, maybe 100mV or something on a ground. RIGHT!!?!?!
I think that is a whole bunch of BS, I chased my tail because of some STUPID odd as heck voltage reading that makes ZERO sense, but is normal. Nissan does NOT tell you the exact voltage just says approx. 5V. So what is approximate then? +/- half a volt on a ECM signal wire?
I think Nissan is stupid, not me. Oh and I'm a Nissan Master Tech, I've ran in to this crap before and it ticks me off. How am I supposed to correctly diagnose a vehicle when you cannot give me good information?
Your thoughts?
So if you see approx. 4.77V on a unplugged ECT on a Nissan that might be normal. Everything else is 5V but NOT on a Nissan. Innovation that excites......oh I was excited.
Remind me - wasn't there some kind of service info problem on the last headache vehicle you had, too? :lol: Trying to figure out what was the bias voltage on a downstream O2 or the like.
Not stupid to expect 5.00V on a thermistor circuit. Just curious, does the 2014 use the same kind of fancy motorized thermostat I found on a Juke recently?
Did you also check the heater hose temps while you were testing? Because, honestly, it kinda sounds like you're fighting a plugged heater core. Better heat off idle, cold at idle. 170 isn't hot, but that should be plenty for the heater. Any evidence of stop leak? Or that someone has been flushing the core recently?
What are you measuring the voltage with ? Temperature sensors aren't supplied by straight 5 v refrence, the voltage you will see unplugged will depend on the input resstance what you are using to measure it. Using a Power Probe or an old analogue AVO meter will show a lower voltage than a decent quality DMM.
Also the coolant temperature is always going to be a fair bit higher than the temperature on the outside of the thermostat housing.
I think you are looking at a coolant circulation issue, air lock or blocked heater matrix or water pump impeller or an aftermarket thermostat that is wrong or defective.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Yes, service info on that one....LOL. I remember that. It is an odd bias voltage around 1.88 volts. That doesn't phase me now.
No fancy water control valve as some other Nissans have. Only a t-stat on the lower hose.
According to the customer the heater core has been flushed. They vacuum filled the system a couple times. Yes, the customer was working on this before it came to me.....more variables to the mix always fun.
I didn't see where the hoses where off the firewall but they did look like they had been off the water distribution box (for lack of a better term) at the top of the cylinder head.
Yes, both hoses where hot, there was a temperature drop across them with the blower motor running.
I feel this is a flow issue and I told the customer that. However as I found, when actual coolant temp is 170 and the ECT is reading 210 on scan tool, we need to fix that first. That could be issue in and of itself, I've saw weirder things.
I mostly want people that may read this to be aware of the wacky NORMAL reference reading when all the rest you can find in easy reach at 5V about on the money.
True, but if the fans are on and the ECT reads 210, the temp on the housing reads 170, and the air the fans is moving is cold......ummm its not that hot.
I agree it could be a circulation issue. Supposedly the system has been vacuum filled more than once. I certainly didn't find air in the system and I checked more than once.
I doubt its a pump issue unless the impeller is slipping on the shaft. A 2014 with long life coolant isn't going to eat an impeller from corrosion in that amount of time and unlike a BMW these are not plastic they are metal.
Customer did put a aftermarket t-stat in it. He was shot gunning parts and trying a lot of things before I saw it. Gotta love the added variables of that!!
I don't know if you still have the vehicle or not? But it might be fun to sub in your own potentiometer for the ECT and make the scan data read what you want. :huh: Get the ECT reading and the infrared thermometer to agree. If you heat then comes back, you're onto something.
Unfortunately I do not have the car. Customer was waiting. However, I did prove the wiring and ECM are completely OK. He said for the cost of a ECT he is going to throw one in it and get back to me. So we shall see.
