Engine Coolant Temperature Sender


I have a 2004 Audi A6 wagon that has an intermittently flashing check engine light. I took it to the dealership to have the codes read and they told me that they got codes for Cylinder 2 and Cylinder 5 misfires. Additionally they got a code saying the Engine Coolant Temperature Sender was electronically faulty. What is this part and what does it do? Is it essential to fix it immediately? The dealership recommended changing the spark plugs and the air filters for the cylinder misfire issue. We are also talking about replacing the timing belt since the car has 105k miles on it. I know there are several other parts that are replaced during the timing belt replacement (like the water pump, thermostat, oil seals, etc). Is it essential to replace these items if there is no immediate need to do so? Just an FYI, the dealership did the diagnostic and gave an estimate, but we are shopping around for an indie mechanic to do the work. Should I be looking for someone that specializes in German imports or can this work be done by anyone?

Mostly any decent mechanic can do this work. If you happen to have someone close who specializes in German cars, go ahead. I wouldn’t go too far out of my way to find one, though.

The reason the waterpump is replaced at the same time as the belt is…it’s driven by the belt, and you have to tear all the way into it to get to it. The additional cost of the water pump, gasket and some coolant is minor when compared to the cost of having a water pump fail, seize and rip your belt apart. At 2000RPM and up, it’ll take a mere second to destroy your engine. It’s worth doing. If the pump fails later, at the minimum, the cost to replace it will still require the belt be removed and replaced.

I’m not sure about the thermostat and seals. I don’t see a need to replace them, but I’m not an Audi specialist, either. Unless the thermostat is buried back there under the belt, I wouldn’t do it…but it’s not an expensive part, either. Doing it wouldn’t hurt anything. Is the engine warming up quickly like it supposed to, and running at the right temps? If not, then it’s a no brainer: replace it.

Engine temp sensor: that sensor tells the computer when the engine is warmed up, so it can cut back on the fuel (an engine at temp requires less fuel than a cold engine). So it should be done. The excess fuel not being burned properly will contribute (over time) to fouling the catalytic converter.

Replacing the plugs and air filter are normal maintenance items. Fouled plugs may partially be a result of the failing temp sensor.

I probably missed something, but I’m not sure what.


Is the water pump something that you can look at and decide whether it needs to be replaced? One shop I talked to said they would change out the pump as a matter of course during the timing belt replacement. The other shop owner said he’d take a more conservative approach and take a “close look” at it once he’s in there and make a decision to replace it or not. Naturally I like the more inexpensive option, but I don’t want that to come back to bite me. We’re only planning on keeping the car another year or so til we pay it off. It has been such a money pit with all of its costly repairs. With two small kids, I need something more reliable.

You can check the condition of the bearing at the moment, but that’s about it. More than that would require it be removed, and if you go that far, why bother putting the old one back on? You’re right back at a gasket, coolant and the work. Saving $20 or so on the pump itself really, truly, isn’t worth the risk.

When I say at the moment, I do mean it, too. You could start it, and it might fail a mile later. You might be fine without replacing it, but I can’t recommend skipping it. I understand saving money…we all want to.

Well one shop quoted $135 for the pump (plus labor) and the other shop quoted $282 for the pump (plus labor). At the second shop, we’re looking at almost $400 to change out the pump. That’s why I don’t want to do it if it’s not absolutely necessary.

I just looked up a pump, and they cost about $85 (plus tax). That’s your over the counter cost, and not at a dealer, for only the part. I think $282 is a tad high, but $135 doesn’t sound too bad. You’r also paying for them to make sure they have the right part, on hand, and ready to be installed in your car. Plus any delivery fees they may have, and storage if they have the parts on hand.

You can take a chance. Make sure you use extended life anti-freeze, and change that out. Making sure you’ve got the best coolant you can would ensure the bearings are at least getting the lubrication they need to last. As long as you’re aware that if it fails, you’re back at the big bill. There’s no guarantee either way.