New member, need help! CEL & overheating!

[nick26]

hey guys,
I just bought an 02 A4 1.8T quattro 5spd w/70K on it.... and the very next day I get it home the check engine light comes on... So I take it to autozone and they tell me the code is P0171 and give me these possibilities:
1. If bank one and 2 codes set together then suspect fuel pressure or MAF
2. O2 sensor defective
3. Ignition misfire
4. Fuel injector problem

So I only had one code which made me skip 1, and assume it was the O2 sensor and got the dealer to give $150 to buy a new O2 sensor. However now that I'm not even sure thats the problem.

My next problem, which is the more URGENT one at the moment is it's overheating badly. I drove it for a week and everything was perfectly fine but last night just as I was getting home the dash beeped saying "coolant" and I look at the temp sensor and it is all the way on H. So this morning I go out there to see if it really is low on coolant and see that it's very full of orange coolant. So I start the car again and let it idle in the driveway for like 20 mins and it gets up to temp but does not go over(the fans did come on though) so I thought maybe it would be ok and start to drive it but I only get a couple blocks away and it starts overheating bad again, so I immediately go home and open the hood, and crack the coolant resovoir and it spews a ton of coolant out the bottom of it. So do I have a bad thermostat? Is the water pump seized?
The dealership is like 3 hours away, and they are a pain in the ass to deal with, so I want to avoid that but if I have to I will take the car back.

[AudiA4Turbo22]

temp sensor! or coolant flange

[nick26]

temp sensor!

you think just the sensor could be bad, and its not really overheating?

or coolant flange

is there any online howtos for replacing this? I haven't found a haynes manual for this car anywhere, do they even make them? or are they worth buying for audi's?

[nick26]

I found this for replacing the temperature sensor: http://www.audiworld.com/tech/eng66.shtml

I guess its a fairly common problem. Seems ridiculous to me that the temperature sensor could be less reliable then the cooling system. How can I make sure the car is not overheating for real? There doesn't seem to be any leaks in the system because the resevoir is full and its not dripping anywhere, and no smoke in my exhaust either.

[quat]

The #1 most common cause of this CEL is a vacuum leak on your intake manifold. Take a look at this tube.

if it is dry rotted it needs to be replaced. Try that. Its cheaper than all the sensors.

[nick26]

The #1 most common cause of this CEL is a vacuum leak on your intake manifold. Take a look at this tube.
if it is dry rotted it needs to be replaced. Try that. Its cheaper than all the sensors.

you were exactly right... that tube was totally cracked and breaking off... i recut the end of it and plugged it back in... i'll go get a new one tomorrow....

as for the overheating, I just replaced the temperature sensor and that did nothing... same behavior... its not smoking or leaking.... I guess I'll try and replace the thermostat tomorrow.

Also i don't know if I'm just being over sensitive now, but now i hear a slight ticking noise while its idling that i don't remember hearing before I was having this problem. Could Something have gotten damaged from the heat that quickly or is this a normal sound?

[quat]

No just get autozone to clear the code and you should be good. whats happening when it over heats? anything? Or does all the coolant boil off? As far as the ticking, check your oil.

[audi4u2nv]

i had he same problem, if its overheating, its the tem sensor

[AudiA4Turbo22]

mine does this sometimes if i turn on the battery my temp guage goes to max!

[A4TL]

the temp sensor can be bad but since it sits at the highest point a simple leak anywhere in the system will force air up there which will do just that.


I'd strongly suggest you look for a leak first since you need to fix that and refill her up with G12 when you put a new sensor on.

the coolant is very sweet smelling and a healthy A4 will have absolutely no coolant smell at all. put your nose to work toucan sam.

[nick26]

No just get autozone to clear the code and you should be good. whats happening when it over heats? anything? Or does all the coolant boil off? As far as the ticking, check your oil.

nothing happens when its overheating... it still runs seemingly fine, i shut it off fairly quickly after the needle hits H because i want to avoid any damage. It's not leaking, because theres not drips or puddles, unless there is a pocket of air in the lines where the leak is, but I doubt it because there is still plenty of fluid in the overflow resevoir. And its NOT the temperature sensor, i just replaced that and took it for a test drive and the same thing happened.

Tomorrow I'll do the thermostat and see what happens.

[A4TL]

sure thats a very time consuming expensive part.

is the water flowing? It's easy to tell if the thermostat is stuck. what codes you pulling?
post em up

how bout you bleed the system first?

Let me know how that thermostat goes. If you buy a new one and it doesn't help i'll buy your old used on off you for cheapz

[nick26]

sure thats a very time consuming expensive part.

is the water flowing? It's easy to tell if the thermostat is stuck. what codes you pulling?
post em up

how bout you bleed the system first?

Let me know how that thermostat goes. If you buy a new one and it doesn't help i'll buy your old used on off you for cheapz

yeah I realize that now, im used to working on fords where its right up front... and it doesn't help that advance auto parts sold me the wrong part apparently. I didn't realize this until I got the thermostat housing open and see this giant spring that looks nothing like what I bought, then i realized the whole box is the thermostat and its not going to be cheap. Regardles, since its all the way out now i guess i'll go to the dealership on monday and get a new one. Anybody know how much then run? $100?

[A4TL]

i think $160 is discounted, so a-hole dealer would be $160-320

its a closed loop thermostat. the ecu has maps so when you hit cruise control and its off boost it can bump up the temps higher to burn more efficiently hence the great mpg on the freeway cruising at 80+

but if you are layin on the gas the ecu will modulate the temps down .

if the gauge feeds a bad signal to the ecu or cluster you will see some whacky stuff. just been there man.

not a cheap part not easy to replace :)

[nick26]

still easier than replacing the water pump it seems... however this is the first time ive seen a thermostat cost more than a water pump on a car... here i thought i would be able to throw in this $13 part to test it and I come to find out its a $160-$320 part.

are there any discount online sites that sell it or is this strictly a dealer only part?

thanks for everyones help by the way...

and heres a good write up for replacing the thermostat, for anyone who comes across this thread in the future:
http://www.audiworld.com/tech/eng106.shtml
and the waterpump(man i hope it doesn't come to this):
http://www.audiworld.com/tech/eng99.shtml

[nick26]

well i found it online here for $90 + shipping:
http://www.trademotion.com/partlocat...=5&catalogid=1

at this point i doubt the thermostat is even the problem though, because i read when they fail they 99% of the time they fail in the open position. So that would only leave the water pump I guess?

[quat]

Check your coolant tubing. At the radiator and in the plenum behind the firewall (next to your battery) find out which ones are warn and which ones are hot. (top/bottom, left/right) this can help you determine where your blockage is. Also how does the coolant flow into your overflow resivior? does it trickle or spurt in steady streams? If it just trickles then I'd lean towards the water pump. I hope for your sake it isn't anything more than the water pump. If its the heater core, or head gasket, then it's a lot more work than the h2o pump. I'm going through the same thing with my 100. I've replaced the pump, and thermostat...still overheating.

There is a restriction somewhere, just gotta find out where.

[A4TL]

what codes do you have? Coolant temp sensor signal too low??? (recalled sensor btw)

[nick26]

Check your coolant tubing. At the radiator and in the plenum behind the firewall (next to your battery) find out which ones are warn and which ones are hot. (top/bottom, left/right) this can help you determine where your blockage is. Also how does the coolant flow into your overflow resivior? does it trickle or spurt in steady streams? If it just trickles then I'd lean towards the water pump. I hope for your sake it isn't anything more than the water pump. If its the heater core, or head gasket, then it's a lot more work than the h2o pump. I'm going through the same thing with my 100. I've replaced the pump, and thermostat...still overheating.

There is a restriction somewhere, just gotta find out where.

I feel your pain, good luck to you...

Well I replaced the thermostat last night and I still have the same problems... I loosened the bleed bolt on the pipe that runs longitudally across the top of the engine and let all the air out and closed it when there was just coolant coming out, so I think I got all the air out of the lines, or is there another bleeder somewhere? Then on the overflow tube not much came out, it just sparactically spurts out, or does nothing at all, definitely not a trickle. I'll try and see which pipes get hotter then others... does anyone have a flow diagram for this system?

[nick26]

what codes do you have? Coolant temp sensor signal too low??? (recalled sensor btw)

The check engine light was on in the first place so i don't know if this overheating issue threw anymore codes and I can't make it to autozone to scan it. Does anyone live by me and have a scan tool or better yet feel like helping change a water pump?

I replaced the coolant temp sensor(the one in the back of the engine), is there another one?

[nick26]

Oh and one more thing i forgot to mention now when I start the car the fans come on a full blast for a minute or two before they shut off, and don't come back on until it starts to overheat. Could the aftermarket(autozone) tempature sensor I put in be causing screwy signals now too?

And thinking about it some more, I wonder if the ticking noise I hear now could be the water pump broken. If it broke like this guys did I would think it would have to make some noise:

By the way I got my thermostat for $144 from my local dealer, so that wasn't as exspensive as i thought it might be.

[dacomb6]

Somehow I am having exactly the same overheating problem on my 2002 1.8t quattro, though I have not tryed to replace the temp sensor as you did, I did manage to replace the thermostat also and still the problem continues. The car will overheat all the way to the H if I pull on it hard or if I drive steady and then when I let off the temp will come back down to 3/4 H. When I replaced my thermostat I had a feel for the blades on the W/P inpeler and the seemed ok. Though later on talking to a friend I had realized that when I was feeling for the blades on the W/P inpeler I was rotating the impeler with my fingers, and I got to the question where is that supposed to happen? Does the W/P impeler have free spin even though the W/P is engaged in the timing belt? Could it be possible for this to happen or would the problem lie there and the W/P is having insufficient capacity to flow the coolant at the nescessary flow? I hope someone with a better knowledge and experiences with these water pumps could chime in to help our overheating problems as I think me might be heading down the same road.

[nick26]

Somehow I am having exactly the same overheating problem on my 2002 1.8t quattro, though I have not tryed to replace the temp sensor as you did, I did manage to replace the thermostat also and still the problem continues. The car will overheat all the way to the H if I pull on it hard or if I drive steady and then when I let off the temp will come back down to 3/4 H. When I replaced my thermostat I had a feel for the blades on the W/P inpeler and the seemed ok. Though later on talking to a friend I had realized that when I was feeling for the blades on the W/P inpeler I was rotating the impeler with my fingers, and I got to the question where is that supposed to happen? Does the W/P impeler have free spin even though the W/P is engaged in the timing belt? Could it be possible for this to happen or would the problem lie there and the W/P is having insufficient capacity to flow the coolant at the nescessary flow? I hope someone with a better knowledge and experiences with these water pumps could chime in to help our overheating problems as I think me might be heading down the same road.

damn i wish i had tried to to feel for the impeller too when i had it off. I didn't know you could reach it. I wouldn't think it should be able to freespin... theres no electronics in it to engage it as far as I know. Maybe it gets engaged like a torque converter or a mechanical fan clutch which fluid in there. I'm about to just replace the water pump as I don't know what else it could be.

[quat]

It shouldn't spin free. New H20 pump for you.

[A4donkey]

nick26, you have not yet tell us what caused the problem (overheat), was that really the water pump impeller?

[nick26]

nick26, you have not yet tell us what caused the problem (overheat), was that really the water pump impeller?

oh yeah sorry, i meant to go back and say... it was definitely the water pump... the impeller inside was stripped and spinning freely.