loyalkipper

Have recently been having trouble starting by 2000 A4 B5 1.8T with 98k miles. It's only happened on two occasions over the past 1.5 months and seems to occur on warmer than usual days - the first time 80F+, the second time 90F+.

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TL;DR

Intermittent starting issues, car cranks but doesn't turn over. Takes 5+ cranks to start. Battery/Alternator/Charging system tested. Battery, Alternator OK. Starter was showing 11volts (low). Have replaced spark plugs recently.

Possible causes after searching - coolant temperature sensor, ignition coils, throttle position sensor, ignition switch etc.
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The Details:


When the issue has occurred the car will crank but won't turn over. There is power as the dash and console light up normally but won't turn over.

The first time it happened, it took 4-5 cranks to get it start, after which in ran fine. That same day, after finally starting the car and driving it again, and letting it sit for an hour, the same issue again. It started up after 4-5 cranks. The battery guage on my dash, when cranking was just under 12volts, and once started it was above 12v. I took the car to Advance Auto to get a battery/alternator/starter test. The battery is healthy, the charging system is fine, no battery drain but the starter test did indicate low voltage of 11ish volts.

I ended up changing my spark plugs with OEM equivalents (Denso). First time @ 98k miles. After changing the plugs, the car started and ran fine for a couple weeks.

Today, the second time, it was in the 90s. It started fine first thing in the morning (70F) but trying to start it again around midday, it wouldn't start after 5+ cranks. It did eventually start when I tried again two hours later or so.

I'm not sure if it's due to weather (failing coolant temperature sensor), the ignition switch, the coils or something more grave.

Any tips would be much appreciated

loyalkipper

The starting issue occurred again today. Started fine in the morning (70F) but when I tried to start it mid afternoon (90F) it wouldn't turn over even after 5-10 cranks. I opened the hood to have a look around, came back about 5 minutes later and it started the first time.

I'm not sure if opening the hood reduced the temperature around CTS or something enough for it "allow" the engine to turn over. Once the car is started it runs and drives perfectly, no rough idle or anything. I'm really confused. It could be the CTS or could even be the crank position sensor. What is more likely?

Thanks

4Driver4

This is a contradiction.
Turning over and cranking are the same thing.

If it doesn't turn over, you have a starter issue.

If it cranks but won't fire, pull and post codes.

If you are convinced that the CTS is at fault (quite possible) just change it. The crank position sensor might also be the issue, but you won't know without codes.

loyalkipper

Sorry. I'm getting my words confused. It does not turnover when I turn the ignition when the issue arises.

I've just picked up a new CTs, it's green. Based on this DIY https://www.audiworld.com/tech/eng47.shtml
it's possible for the CTS to be blue, green, and black. Aside from potentially not physically fitting, would there be an issue installing a CTS that doesn't match the original color, assuming it fits?

As I think the issue is temperature/weather related, I think it is a faulty CTS, but you mentioned a faulty starter. Does warm weather adversely affect a starter?

When I got the battery/charging system/alternator/starter tested at Advanced Auto, for the starter test, it did say low voltage (~11v). Mind you this was on a hot day, the same day I had starting issues.

In terms of coolant, I understand the Audi needs G12 and is orange, I couldn't find any G12 coolant at Advance Auto specifically, but did see orange coolant, will a generic orange coolant suffice?

Thanks

AudiMick

No generic , if you can't find G12 just top up with distilled.

It's not the CTS if it won't turn over. 11 volts is way too low.Battery should be 13+ volts and above 14 when charging from alternator.You may have a bad cell.

4Driver4

You have a bad alternator. The CTS does not impact the starter circuit.

loyalkipper

I just changed the CTS over the weekend, the original was well worn. The car failed to start later today although it did start in the morning. Today's temp was around 85F. Either it's temperature related or just coincidental. The car did start eventually, I initially turned the key 4-5 times. I left the car for a couple minutes (under 5) and when I came back and tried again, it started right up on the first try.

Is this fueling issue or perhaps ignition coils now? The car drives fine when its running, no stuttering. I wonder if failing coils only show during the starting process or whilst the engine is running.


As for the battery and alternator, I had them tested at Advance Auto when starting issues started. They said the battery, alternator, and charging system were all healthy. I may have not phrased my original post properly, when the car does have trouble starting, the battery gauge shows just under 12v volts when the key is turned/cranked. When the car does start, the battery gauge shows it is charging 13-14 volts.

loyalkipper

From what I had read, a failing CTS will either give artificially high or low coolant temperature readings to computer and force a hard start procedure (no choke) at least when the coolant temperature is "high."

4Driver4

True enough. But you've stated that the issue is that the engine does not turn over. Cts has no effect on turning over, only on starting.

loyalkipper

Maybe I'm getting my terms mixed up, it does turnover, it just doesn't start. With that said, the CTS could be an issue, but seeing as I've just replaced it and the issue persists its likely something else. I'm confident it's weather/temperature related. I think it could be ignition coils or crank position sensor. Are crank position sensors prone to failing during hot weather?

I also do not think it's ignition switch related since the starter motor definitely cranks.