Please help. My daily driver is spontaneously messed up.

[andrew.k]

Guys, OG & Diagnosticator.

Please shed some insight on my issue if you can.

For the last few months my A4 has been running great, other than a brake light switch that failed, which wasn’t a huge deal.
Now here is where the fun starts.

On Monday I got a check engine light on the way to a business meeting, I thought of it as nothing as we all usually do with these cars, small sensor in which vag-com will enlighten us later. After my meeting I went to a friends shop to diagnose the CEL and it turned out to be a G62 Coolant Sensor (Engine Temperature to Low). In turn I went to the dealership to pick one up. When I got home, I popped off the 3-way hose at the rear of the engine and changed the G62 sensor (lots of coolant spilled out). I then topped up the coolant, reset the codes and called it a day.

Next day I woke up to go to work and the car starts up at 10inhg and bounces around, really rough idle. It has never done this before, then settles to 19 instead of 21inhg where it usually was. Being somewhat familiar with Audi’s this usually indicates a vacuum/boost leak. I though that maybe I cracked the breather hose at the top or something else.
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Pic borrowed from A4Mods (mine was in tact)
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Pressure tested the system until the oil was bubbling, and had to two people listen for leaks….nothing. So I tried propane, engine idle never changed. No leak at all. While I was down there I deleted the N249, and it does hold boost a little better, but that definitely wasn’t the problem.

I changed the plugs; (BK6’s) & visually inspected the coils, purged the fuel rail, all fine. The last thing I checked was the MAF, unplugged it and there was a fluctuation in engine idle, so I’m assuming that it works. I am completely stumped. I now get a traction lamp on top of the CEL saying that it doesn’t receive a signal from the ECU, engine idle is 100RPM higher than it normally is, radiator fans always turn on (I’m thinking as a failsafe), temperature gauge doesn’t go up to 90F like it used to (when hot it sits at 75F on the dial). The G62 code came back. I can’t remember all the code numbers off the top of my head, but I will update this thread when I get home and scan the car again. This is my daily driver; I need to get this fixed. Any advice would be greatly appreciated.

Tid Bits:
Car boosts to full PSI WOT
When warm idles 100RPM higher than usual but at the correct vacuum 19-21inhg
Old plugs had been fouled (gapped to .28 – BK6’s) – 5000kms on them
Radiator fans turn on right away – turn off when the cars warm (They never used to turn on on start-up for no reason)
Mod’s are listed in my signature if that helps, but I have been running them for over a year successfully until now.
Reasons for still getting the G62 code: No clue, is there another one?
Reason for the traction lamp: No clue
Reason for getting a knock sensor: Probably because it’s acting erratically
Reason for temp being off: Spontaneous mood of the thermostat due to all this shit?

[A4Maine-iac]

Did you have the above issues with the old CTS in there? If not . Throw the old one in there. Might have gotten a bad one. Other CTS is under the radiator drivers side. But dought you would get all that action. Also check the wiring to CTS.
Here is some info. I assume its this code.
16501/P0117 - Engine Coolant Temperature Sensor (G62): Signal too Low
Possible Symptoms

* Difficulties with starting a cold engine.
* Starting the engine when engine is warmish or warm, idle rpm immediately is 1200 - 3000 rpm.
* RPM at idle is irregular.
* With all engine temperatures seldom idle rpm will vary between 900 - 1000 rpm.
* With engine warm (90 °C) the engine temperature suddenly drops (70 °C) and slowly comes back to 90 °C.
* Bad acceleration during warming up.
o Diesel: an indication is extreme long time burning time of the glow indication light.

Possible Causes

* The electrical signal coming from G62 is too low
* Wiring and/or connections faulty (short circuit?)
* Engine Coolant Temperature Sensor (G62) faulty

Possible Solutions

* Check wiring and connections
* Check / Replace Engine Coolant Temperature Sensor (G62)

[andrew.k]

I will go to the dealership and grab another G62.
Seems rather odd that the sensor wouldn't work, I took a look at the wiring and it looked good. The only thing I can think of that may have to do with the wiring is maybe I caused a short and a fuse blew.

Does anyone know of a fuse co-related to the G62?
Does the sensor under the drivers side radiator contribute to the how the gauge operates? Are they both identical?

I would rather buy two of these and try to corner the problem.

Thanks for the continued insight.

[Charles.waite]

I will go to the dealership and grab another G62.
Seems rather odd that the sensor wouldn't work, I took a look at the wiring and it looked good. The only thing I can think of that may have to do with the wiring is maybe I caused a short and a fuse blew.

Does anyone know of a fuse co-related to the G62?
Does the sensor under the drivers side radiator contribute to the how the gauge operates? Are they both identical?

I would rather buy two of these and try to corner the problem.

Thanks for the continued insight.

If you have a multimeter you can test the resistance across the pins of the G62 so see if its actually working rather than just assume its faulty.

I've got on sitting on my desk at home, i can test it to see the resistance at room temp for you if you want during my lunch break.

Did you get all the air out of the coolant system? Could be a big bubble localised around the CTS causing erratic readings. Did you fully remove the rear flange? or just the CTS from the flange?

[andrew.k]

If you have a multimeter you can test the resistance across the pins of the G62 so see if its actually working rather than just assume its faulty.

I've got on sitting on my desk at home, i can test it to see the resistance at room temp for you if you want during my lunch break.

Did you get all the air out of the coolant system? Could be a big bubble localised around the CTS causing erratic readings. Did you fully remove the rear flange? or just the CTS from the flange?

I do have a muti-meter, and if you could do so, I would compare it to my old one I threw out as well as the new one I installed.

I have bled the system with the little screw on top, but I'm not entirely sure if it cured all the bubbles in the system. Perhaps that’s why the system is malfunctioning and the sensor is "colder" than it should be. I will try to bleed it again tonight.

I didn’t remove the rear flange; I could barely fit my hand in there to get the old CTS out. I took out the old green sensor along with the o-ring, and put in the new one in. How does the whole flange come out?

[Charles.waite]

Its a real bitch. Theres a DIY on here for it in the tech section. I've got to replace mine soon so I'll probably be tackling it in the next few weeks... yay...

So I measured the resistance across the pins and heres what I got:

   _________
  /         |
 / 1     3  |
|   |   |   |
|           |
|           |
|   |   |   |
 \ 2     4  |
  \_________|

ASCII art is awesome...

Anyway between pins 1 & 2 you should get about 2.86KOhms of resistance and between 3 & 4 you should get 1.3 KOhms. This is at about 60*F (They'd been sitting in my house with the heat off, the house thermostat said 60*F). Notice the orientation of the Connector, its a backwards D.

[CrazyCal]

My money is on air in the coolant. Air in the coolant can cause all kinds of odd readings and idle issues. Might try bleeding from the"bleeder hole" pictured below. It's the highest point in the coolant system. Read this thread for reference: Clickity Click

[dubgli]

interesting.. i never knew air in the coolant could affect the idling/evap system. I'll have to keep that in mind.

Sporadic idling would most likely be what you stated, a vacuum leak or bad maf. So you already pulled the maf and the idle is still crap so it's not the MAF..

Old guy would suggest clamping each evap hose one at a time to see if you hear an improvement in the idle. This could help locate the vacuum leak better than a boost leak test. I use vice grip pliers.

[andrew.k]

I will bleed the system through that line before replacing the unit.

Thanks a bunch.

I re scanned codes today and I believe my MAF is on its way out or has already done so.

VCDS-Lite Version: Release 1.0
Wednesday, 14 March 2012, 20:16:06:0


Chassis Type: 8E - Audi A4 B6/B7
Scan: 01,02,03,08,09,0F,11,15,16,17,18,36,37,45,46,55,56 ,57,65,67,69,75,76,77

************************************************** ************************************************** ************************************************** ******-
Address 01: Engine Labels: Redir Fail!
Controller: 8E0 909 518 AF
Component: 1.8L R4/5VT G 0003
Coding: 0016701
Shop #: WSC 79153
1 Fault Found:
16486 - Mass Air Flow Sensor (G70): Signal too Low
P0102 - 002 - Lower Limit Exceeded
Readiness: 0100 1101

************************************************** ************************************************** ************************************************** ******-
Address 03: ABS Brakes Labels: 8E0-614-517.LBL
Controller: 8E0 614 517 H
Component: ABS/ESP allrad 2328
Coding: 04275
Shop #: WSC 06435
1 Fault Found:
18265 - Load Signal: Error Message from ECU
P1857 - 35-00 - -

I will be ordering a new MAF tomorrow.
http://www.ecstuning.com/Audi-B6_A4-...nsor/ES517741/

Will that one suffice?

[CrazyCal]

Are you sure you need a new MAF? Try cleaning it first.

[dubgli]

Are you sure you need a new MAF? Try cleaning it first.

i 2nd this.. If it is the MAF, when you unplug it the idle should get better. Even if your MAF is bad, this just means your MAF is bad and you still have another issue..

[andrew.k]

Are you sure you need a new MAF? Try cleaning it first.

I did try cleaning it, it somehow broke overnight, I read the readings through vag-com, and it read 0 G's. I'll pick one up, and post the result's as soon as I can.

[andrew.k]

A quick update with a few questions.

I picked up a new MAF and the CEL & Traction light seem to have disappeared. Although the car ran much better without the MAF, I'm guessing the ECU has to re learn the readings, or is there some sort of adaption in vag-com I can do to speed up the process? (Car stutters in 1st/2nd low RMP WOT)

That aside, I still have the coolant temp problem. I bled the system again last night, including the heater core.
As stated previously, I changed the upper CTS by the back of the engine. Now I have little or no reading on the temp gauge inside and no heat.

As old guy said in another thread.

The thermostat is a MAP controlled thermostat. The plug is not a sensor. It is a wax heater controlled by the ECM which allows the ECM to over ride the mechanical portion by applying power to the heater and forcing the thermostat to open if certain conditions exist.

Is it possible that this upper sensor is faulty and is keeping the thermostat open? Or is that controlled by the sensor at the bottom of the radiator?

I would rather change the lower sensor then the thermostat, especially because I had no issues with it before replacing the rear CTS.

[boy412]

Replacing the lower sensor would take all of 5 minutes, and its a cheap enough part. Easy to rule that out as the culprit...

[Charles.waite]

If you have a vagcom, check out measuring blocks 130-132. Its all the coolant related temps and whatnot. Might help narrow down the culprit.

[andrew.k]

If you have a vagcom, check out measuring blocks 130-132. Its all the coolant related temps and whatnot. Might help narrow down the culprit.

Will do, thanks for the continued due-diligence Charles.

I will catch this gremlin sooner or later.

[TehC0de]

So you said the car ran much better without the MAF, but still had some stuttering during idle? That could also point to a crack or leak from your crank case breather. I had a similiar issue a few months back. Start up was rough occasionally and idle RPM's were a 100 or so higher than norm at times, and for an example at a red light or anytime i stopped after the car was warm, the car would basically cough or stutter for a split second every now and then.

Turned out I had a cracked crank case breather, that was a nifty 600$ with labor to replace at the stealership >.<

[CrazyCal]

So you said the car ran much better without the MAF, but still had some stuttering during idle? That could also point to a crack or leak from your crank case breather. I had a similiar issue a few months back. Start up was rough occasionally and idle RPM's were a 100 or so higher than norm at times, and for an example at a red light or anytime i stopped after the car was warm, the car would basically cough or stutter for a split second every now and then.

Turned out I had a cracked crank case breather, that was a nifty 600$ with labor to replace at the stealership >.<

Are you kidding $600 for a crank case breather replacement? OMG

[TehC0de]

Let me emphasize the *****Stealership*****

[CrazyCal]

Let me emphasize the *****Stealership*****

Just slapped this together. I think it gets the point across.

[dubgli]

wow.. $600? i'm sure we will all DIY now.

[andrew.k]

Update: I changed the front lower sensor under the rad, and the fans no longer turn on at start up, although the car takes really long to get up to the 90*.

I think that the thermostat is working, because when I push the gas, the temp needle goes down, meaning that it's opening to keep the engine cool, but then why does it take so long to warm up.

Does the thermostat slowly break or is it a component that either works or doesn't. Does anyone know?

[Charles.waite]

Update: I changed the front lower sensor under the rad, and the fans no longer turn on at start up, although the car takes really long to get up to the 90*.

I think that the thermostat is working, because when I push the gas, the temp needle goes down, meaning that it's opening to keep the engine cool, but then why does it take so long to warm up.

Does the thermostat slowly break or is it a component that either works or doesn't. Does anyone know?

Your T-Stat isn't working. The needle should never drop under load under any circumstances. My B7 had slow warmup (15+ minute) and would fluctuate in temp from 1/2 to 1/4 and back frequently. When I replaced my T-Stat it all went away. When I tested my old T-Stat in boiling water, I found it was closed at room temp, but it began to open at 50*C. Its supposed to open at 80-85*C. Until that point its supposed to be closed tight. Yours sounds like its failed int he exact same way as mine.

FYI when I had no leaks from it. And when I removed it, upon visual inspection it seemed to be absolutely fine. It wasn't until later, when I tested it that I found it was opening WAY to early.

I would replace the T-stat and I would bet $$$ that your problem will go away.

[andrew.k]

I have a feeling your right, pointless spending $100 on the two oem sensors.
Didn't solve anything, so I'm ordering the T-Stat from Audi today.

I find it strange how they can still open and close but not to the operating specs.

Thanks Charles.

[Charles.waite]

I have a feeling your right, pointless spending $100 on the two oem sensors.
Didn't solve anything, so I'm ordering the T-Stat from Audi today.

I find it strange how they can still open and close but not to the operating specs.

Thanks Charles.

NP.

Yea I thought it was weird too. I have a pic of hte new one and old one side by side, the old one looks absolutely fine and was tightly closed at ambient temps (40*F, it was cold out!) but the boiling water test was the giveaway that it was opening prematurely. Seems really annoying that it can fail that way, but its probable the "wax motor" thing was worn out and not operating right.

[andrew.k]

Problem is finally fixed, I'm posting because I know someone will want a conclusion to this thread eventually.

I got around to going to the dealership grabbing a new t-stat as well as replacing the "new" defective green cts sensor and voila, everything works like a charm.

I get heat in my cabin in 5-10 min, temp needle steadily rises to 90*F, no more miss fires on start up, rough idle, loud fans turning on. Wow, two little things can cause such misery.

Thanks for all the help & to Neil @ Owasco Audi for the parts.

[waldo1324]

awesome to hear.. did you h ave a part # for the tstat and price?

[andrew.k]

awesome to hear.. did you h ave a part # for the tstat and price?

part # 06B-121-111K Depending on dealership $140-160.

[dewey527]

Reviving a thread but looks like I will be replacing the rear CTS. After doing a TBA all hell seemed to rear it's ugly head. Weird how things of no relevance seem to pop up when working on this car...Next morning the car took 8-10 cranks to fire up, fans sounded like jet engines and the idle was at 1k. Had trouble starting the car leaving work and would die instantly once I tried engaging the clutch. Scanned when I got home and got 16501 and 17987. Did another alignment and was successful but still have 16501. Funny thing is I had ordered some oil filters and coil packs and added a lower temp sensor on a hunch a few weeks back - wrong! So I ordered a green CTS and will try to replace over wknd... I don't have any leaks and the flange was replaced a few years back. should I replace the flange at the same time? The car gets to temp within 5 or so minutes, I have heat and the gauge doesn't waiver from the middle. That would eliminate the need to replace the t-stat right?

[coowhip]

Replace the sensor. clear the Codes. Chances are its not the T-stat.

[dewey527]

Thx - if only it was easy as that!

[p8nt]

Necrobumping this thread due to recently getting this code: 16501/P0117 - Engine Coolant Temperature Sensor (G62): Signal too Low

I realize it comes down to CTS or Tstat, just hoping I can avoid guessing and replacing the wrong part.

I'm leaning Tstat due to the fact that the car is taking FOREVER to warm up. Any flaws in my assumption?

[coowhip]

Replacement them all. In my opinion it should be a trifecta repair, both CTS's and the thermostat. Maybe coolant reservoir and a full flush.