Hi
I have a 2004 TL and have noticed a slight error over the last few weeks with the heating system.
Assuming an outside temp of around 0 C (32 F).
When i set the temp at 22 C (72 F) the car will heat up to a comfortable temperature, but then after a while i start feeling cold. I have noticed that cold air will be flowing from the vents. I have sometimes needed to raise the temp to almost 26 C (79 F) or 28 C (82 F) before heat will start flowing again.
Can anyone suggest what might be the problem.
Thanks
AKSAKS

 

You're not alone, I've noticed this on my '04 as well. I've always just cranked up the temp, but it's annoying to have to do that. Hope someone else has a solution....

and for me, it's only the heat. When running the A/C, I never get hot and have to adjust the temp like I do for the heater.

 

Our TL is the same, especially on the passenger side. It seems as though it doesn't maintain the same cabin temp as the settings need to be adjusted upwards after a period of time. The other night on the way home from Atlantic City both settings were (auto) 72, but 45 minutes into the drive, the wife's was up to 78 and she even put the heated seat on low to stay comfortable.
Never had a problem like this with any of the other climate control systems we've owned.

 

Hmmm....that's 3 so far. What year? Nav?

 

ive never noticed this in my 04 but now ill pay attention you guys just made me paranoid.... because i can imagine how much the stealership is going to charge to repair this problem especially if you're not covered under warranty anymore

 

'04 Nav. It's a CPO car and I purchased the bumper to bumper warranty when purchased a couple of years ago.
We don't use the car very much, but I better start checking the FSM for any info.
It's is just like stated above, cool air flows from the ducts when in auto.

 

AKSAKS,

Do you have Navi?

 

No, mine is a 2004 TL without the Navi.

 

Check your coolant level.. if it's low.. check for dampness near on the inner passenger carpet to indicate a bad heater core.. check the heater control valve at the rear of the firewall and look for coolant leaks.

I had this happen to me a couple times. Then noticed coolant reservoir was empty and no coolant at top of radiator.. found a coolant leak at the heater control valve.. hopefully that's all it is.. going to be replacing the valve & inlet pipes very soon.

 

Nope, no coolant leaks for me. Had it flushed and refilled at 60K. Only had to add about 1/2 quart in the first 60K. Now at 73K and level hasn't changed since the flush/refill.

Heater core is getting hot, plenty of heat available....I think it's somethiing in the sensors for the climate control....

 

I agree, and also have never added any coolant since we've owned the car. When started cold and during warmup, nice and hot as in cabin temp comes up as required, but after a period of time the cooler air starts flowing and then the settings need to be raised, not a degree or two, but quite significantly to get the cabin warm again.
Next time we're out in the car, I'm going to take the stick thermometer and see exactly what the air temp is at the vents, and when it changes.

Just tried the self diagnostic check, no codes either side.

 

Hmmm. I'll have to give a try. Then I'm going to pull the temp sensor and run the resistance check on it.

AKSAKS,

Trying running the diagnostic test as well. To run the test, turn ignition switch to on, hold OFF switch down and press the recirculate button 5 time within 10 seconds. The test will run and then the results will be displayed in the driver and passenger side temperature led readout. If 88 is displayed in both, there is no fault. If only a segment of one of the leds is displayed, that indicates a fault.

 

Yeah, that checks for me also. I have to raise the temp at least 5 degrees before I get hot air again....I'm betting it's a faulty interior temp sensor..The resistance check will tell.....

 

Oops, my bad. If there is a fault, it will alternate 88 and the segment/s showing the fault.

Nothing will be displayed in the temp windows if there is no fault.

I ran the test and it only ran for about 30 seconds ("Lo" showed in the temp windows during the entire test before shutting off the fan) and then the display went blank. I assume that means no fault.

Next is the resistance check...

 

Add me to that list. 04 TL, no Nav. I have to crank the heat up to get the hot air flowing, then I can move it back down to a reasonable temp and it will moderate just fine after that.

 

Here's scans from the service manual for two sensor diagnostic checks you can run:

 

I ran the two diagnostic tests and no faults were noted.

Then I ran the ohm check on the in-car temp sensor. At 19F it read 6700ohm and at 68F it read 1650ohm, so it's reading about 10-15F too high, with the higher spread at room temp. That would explain why it gets cold. It's telling the HVAC system that the interior temp is warmer that it actually is.

This also would seem to confirm the ambient temp reading during the sensor input display test. It gave me a reading of 9C, which comes out to 48F. I keep my garage at 40F.

The sensor is only $21.25 plus shipping, so I think I'm going to order it. Anyone have any other suggestions?

Part# 80530-S2R-941

 

So far, great work. I guess I'll sit back and wait to see the outcome if/when a new sensor is installed.

 

Ok I ran the tests.
On the first test, no part of the 88 was lit.
The second test is as follows:

Temp originally set at 22 C.

1-18
2-13
3-01
4-74
5-02
6-51
7-53
8-00 (i was parked)
9-34

AKSAKS

 

So, according to that test, it was warmer inside the car than outside. Does that seem right? Do you think it was as warm as 18 in the car? If no, then you could have the same issue I do where the temp sensor is reading high.

 

I believe this is normal for the 3G TL. Both of mine do this. And I think the reason is this.

Once proper cabin temperature is reached, vents will begin to emit cooler air to help keep the driver awake. If you set the the dash and floor vents to flow (must use the manual mode and not AUTO for this), you will notice slightly cooler air coming from the center vents than that which emits from the floor vents.

The fix is simple, quick, and free. Either significantly reduce the flow to the side vents, or close them all together in the cooler months. And avoid using the AUTO setting in the cooler months.. instead, use the manual setting. You will find the interior temperature to remain more pleasant this way.

Anyway, this is what I do with my '04 TL manual.

 

The fix is accurate, been there done that, but the cause is annoying. Why have a climate control system that needs to be manually adjusted, it doesn't make sense. Poor design if that certainly is the case. It will definitely keep you awake as you might even freeze to death in the car if the temp isn't raised.

Looks like another negative for the TL.

In all the climate control systems, or zone control systems we've had, after a period of time, under certain conditions, the system goes into a bilevel mode to supply fresh dry air into the cabin through the upper vents while continuing to have heated air flow at the floor, but also to maintain the preset temperature, which is not the case with the TL.