Hot start failure diagnosis
05-17-2013, 03:26 PM
#21
AudiWorld Member
Thread Starter
Photos associate with text *above* not below. Start by releasing the coolant reservoir and shifting forward. No need to drain, but do release the level sensor connector on the bottom.
The grey male & female connectors are the harness and sensor side connectors, respectively. The lower half clips inside that awkwardly located bracket, with the stupid clip that prevents convenient removal.
To access that blasted bracket, remove the aluminum heat shield...the tab on the driver's side releases with a gentle pull, and the tab toward the passenger side requires the plastic button in the center of the tab to be gently shifted toward the driver's side. The heat shield can be removed with a bit of wiggling, exposing the ridiculously well-secured connectors.
I did not remove any SAI system components, but it would've made for a less expletive-laden repair.
http://www.imagebam.com/image/f859cf255049400
Once this pain-in-the-*** is exposed, finger pressure may be sufficient to detach the connector from the bracket. Alternatively, use a set of bent-tip needlenose pliers to grasp the driver's side of the bracket next to the connector, and insult its lineage counterclockwise to force the small, yet fierce, square tab from the channel in the lower half of the connector. Once that Tourette's-inducing tab is released, crack open a beer...that was the hard part.
http://www.imagebam.com/image/64a260255049405
Under the driver's side of the car, locate the small hole (it's roughly hand-sized, if you have little carny hands like me) between the inner CV joint, transmission, and turbo. Use the shape of the new sensor as a reference, and hunt for the old sensor just out of sight, at about two o'clock on the transmission if viewed from the front. The 10mm bolt is a good reference. The wrench in this picture is about 5" long, and it's possible to swing it 180 degrees in that space. A longer ratchet wrench would not fit, nor will a standard ratchet--oil and coolant lines to the turbo interfere. THE WRENCH IS SECURED ON THE 10MM BOLT IN THIS PHOTO.
http://www.imagebam.com/image/3fea13255049410
Old sensor, by Bosch. This one lasted 140k+ miles.
http://www.imagebam.com/image/630302255049413
Another angle on the old sensor. Pull the spacer off, it's important.
http://www.imagebam.com/image/875786255049415
Checking size, new vs old...an old thread I found on this repair mentioned the new sensor being too long, later posts revealed the owner forgot to swap the spacer to the new sensor, but it was worth looking.
http://www.imagebam.com/image/4a5c2d255049417
Spacer removed from old sensor.
http://www.imagebam.com/image/8c64af255049419
Installing the new sensor. Wrap the heat shield piece around the wire, drop it down the hole on the passenger side of that !@#$ing bracket, guiding the sensor by hand as the magnet will stick to everything on the way in, secure the connector at the top (don't plug it in yet), make your way under the car, and install the new sensor.
NOTE THERE ARE TWO HOLES of similar size, within an inch or so of each other, on the transmission. The hole you want is finger-sized, -ish, with a flat surface around it and an offset smaller hole. The larger hole is to the front, smaller hole to the rear. The *wrong* hole is also finger-sized, it is to the rear of the other two holes, and has a narrow flange leading away from it, and if you stick the sensor in there, it will complain that this isn't Tijuana and then it will call the bouncer and you will get thrown out on your ***.
Working again from above, route the wire as far toward the centerline as possible before running horizontal to the harness-side connector; this is to keep the wire and heat shield as far from the turbine as possible. The connector installs back in that stupid @!#@ing bracket with the rounded side facing out, and mind you engage the correct channel on the lower half of the connector.
Reinstall the small aluminum heat shield, and you're done with the new sensor.
http://www.imagebam.com/image/a09981255049422
One more shot, showing the heat shield wrap in place. Once the new sensor is routed and installed, cut the line on the factory sensor and remove it. It's not possible to pull either the connector or the sensor through the gap between the coolant pipe and the block, where it's routed from the factory.
http://www.imagebam.com/image/a480ed255049425
For a first time, not knowing exactly where I was looking and doing a lot of this via guesswork, this was easily a three beer job. In the future, I'll just replace this sensor with the timing belt/water pump, and it'll probably take an hour tops, from wheels up to wheels down. Hopefully the photos and descriptions speed up someone else's repair.
-Sean
The grey male & female connectors are the harness and sensor side connectors, respectively. The lower half clips inside that awkwardly located bracket, with the stupid clip that prevents convenient removal.
To access that blasted bracket, remove the aluminum heat shield...the tab on the driver's side releases with a gentle pull, and the tab toward the passenger side requires the plastic button in the center of the tab to be gently shifted toward the driver's side. The heat shield can be removed with a bit of wiggling, exposing the ridiculously well-secured connectors.
I did not remove any SAI system components, but it would've made for a less expletive-laden repair.
http://www.imagebam.com/image/f859cf255049400
Once this pain-in-the-*** is exposed, finger pressure may be sufficient to detach the connector from the bracket. Alternatively, use a set of bent-tip needlenose pliers to grasp the driver's side of the bracket next to the connector, and insult its lineage counterclockwise to force the small, yet fierce, square tab from the channel in the lower half of the connector. Once that Tourette's-inducing tab is released, crack open a beer...that was the hard part.
http://www.imagebam.com/image/64a260255049405
Under the driver's side of the car, locate the small hole (it's roughly hand-sized, if you have little carny hands like me) between the inner CV joint, transmission, and turbo. Use the shape of the new sensor as a reference, and hunt for the old sensor just out of sight, at about two o'clock on the transmission if viewed from the front. The 10mm bolt is a good reference. The wrench in this picture is about 5" long, and it's possible to swing it 180 degrees in that space. A longer ratchet wrench would not fit, nor will a standard ratchet--oil and coolant lines to the turbo interfere. THE WRENCH IS SECURED ON THE 10MM BOLT IN THIS PHOTO.
http://www.imagebam.com/image/3fea13255049410
Old sensor, by Bosch. This one lasted 140k+ miles.
http://www.imagebam.com/image/630302255049413
Another angle on the old sensor. Pull the spacer off, it's important.
http://www.imagebam.com/image/875786255049415
Checking size, new vs old...an old thread I found on this repair mentioned the new sensor being too long, later posts revealed the owner forgot to swap the spacer to the new sensor, but it was worth looking.
http://www.imagebam.com/image/4a5c2d255049417
Spacer removed from old sensor.
http://www.imagebam.com/image/8c64af255049419
Installing the new sensor. Wrap the heat shield piece around the wire, drop it down the hole on the passenger side of that !@#$ing bracket, guiding the sensor by hand as the magnet will stick to everything on the way in, secure the connector at the top (don't plug it in yet), make your way under the car, and install the new sensor.
NOTE THERE ARE TWO HOLES of similar size, within an inch or so of each other, on the transmission. The hole you want is finger-sized, -ish, with a flat surface around it and an offset smaller hole. The larger hole is to the front, smaller hole to the rear. The *wrong* hole is also finger-sized, it is to the rear of the other two holes, and has a narrow flange leading away from it, and if you stick the sensor in there, it will complain that this isn't Tijuana and then it will call the bouncer and you will get thrown out on your ***.
Working again from above, route the wire as far toward the centerline as possible before running horizontal to the harness-side connector; this is to keep the wire and heat shield as far from the turbine as possible. The connector installs back in that stupid @!#@ing bracket with the rounded side facing out, and mind you engage the correct channel on the lower half of the connector.
Reinstall the small aluminum heat shield, and you're done with the new sensor.
http://www.imagebam.com/image/a09981255049422
One more shot, showing the heat shield wrap in place. Once the new sensor is routed and installed, cut the line on the factory sensor and remove it. It's not possible to pull either the connector or the sensor through the gap between the coolant pipe and the block, where it's routed from the factory.
http://www.imagebam.com/image/a480ed255049425
For a first time, not knowing exactly where I was looking and doing a lot of this via guesswork, this was easily a three beer job. In the future, I'll just replace this sensor with the timing belt/water pump, and it'll probably take an hour tops, from wheels up to wheels down. Hopefully the photos and descriptions speed up someone else's repair.
-Sean
Last edited by devinsixtyseven; 05-17-2013 at 03:36 PM.
05-17-2013, 04:45 PM
#22
AudiWorld Member
Thread Starter
Yup! My money is still on the CTS. Remember that there are two on the 2.7. One for the gauge and one for the CPU. CPU is on the passenger side aft (sorry, old submarine sailor)of the head. Won't throw a code, but will NOT start when warm. Dumps black smoke out the exhaust trying. At least that's my experience. Hope yours is as simple.
05-18-2013, 06:46 AM
#23
AudiWorld Super User
Just occurred to me, the black smoke thing happened along with rough idle when the CTS did go. Mine threw a code, at least, and lit the CEL. Might be a difference in model years? Mine's an 04, and the faulty CTS threw a code that came up as a coolant temperature sensor when read with the Torque app on my cell phone.
10-17-2013, 12:53 PM
#24
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For the record, the symptoms I described (rough idle, no hot start, etc) existed when the factory CTS failed, and disappeared with the new (green) CTS.
Information at Ross-Tech mentions the camshaft codes are likely to trigger with a bad G28, and my car's symptoms match others with a G28 failure.
I'll update post-fix.
Information at Ross-Tech mentions the camshaft codes are likely to trigger with a bad G28, and my car's symptoms match others with a G28 failure.
I'll update post-fix.
10-17-2013, 04:30 PM
#25
AudiWorld Super User
If you're going to start throwing parts at it, don't go any further than replacing the coolant temp sensor. At least it's cheap and fairly easy to DIY.
10-18-2013, 10:24 AM
#26
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Any other input is welcome. thanks
10-22-2013, 07:27 AM
#27
AudiWorld Senior Member
I recently replaced my speed sensor. Car started cold fine. But often did not start after being driven for 30+ minutes, then siting for 30+ min. If I waited another 30 to 60 min it would start. It did once throw the code for a bad speed sensor, but not always. I figured it was intermittent and going south.
I had driven to the shop to buy the part intending to do it myself. But it would not start when I tried to leave. I sat in their parking lot waiting for the 30-60 minutes it usually took for the car to start. Was told by my tech to check for the engine RPM readout on VCDS (block 4 I think) when cranking. If the speed sensor was not bad the RPMs would show (200 to 400?) as the starter cranked and that meant I had another problem instead. If speed sensor was bad then there would not be a reading.
I never found out if this was true as when I set up to monitor the RPMs on VCDS and engaged the starter the RPMs showed and the car started. This was after sitting about 75 minutes with a no start. When it started I decided to have them replace the part. I was there and tired of the mess and did not feel like crawling under the car on 8" ramps when I got home. Glad I let them do it. It was not all that easy to access and was stubborn to remove.
Also interesting to note that only one time did I get a code about the G28 being intermittent. I reset it and continued to have problems with hot starts, no codes about the G28 came up again. Although replacing the CPS has resolved my problem.
I had driven to the shop to buy the part intending to do it myself. But it would not start when I tried to leave. I sat in their parking lot waiting for the 30-60 minutes it usually took for the car to start. Was told by my tech to check for the engine RPM readout on VCDS (block 4 I think) when cranking. If the speed sensor was not bad the RPMs would show (200 to 400?) as the starter cranked and that meant I had another problem instead. If speed sensor was bad then there would not be a reading.
I never found out if this was true as when I set up to monitor the RPMs on VCDS and engaged the starter the RPMs showed and the car started. This was after sitting about 75 minutes with a no start. When it started I decided to have them replace the part. I was there and tired of the mess and did not feel like crawling under the car on 8" ramps when I got home. Glad I let them do it. It was not all that easy to access and was stubborn to remove.
Also interesting to note that only one time did I get a code about the G28 being intermittent. I reset it and continued to have problems with hot starts, no codes about the G28 came up again. Although replacing the CPS has resolved my problem.
10-28-2013, 07:41 AM
#28
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I recently replaced my speed sensor. Car started cold fine. But often did not start after being driven for 30+ minutes, then siting for 30+ min. If I waited another 30 to 60 min it would start. It did once throw the code for a bad speed sensor, but not always. I figured it was intermittent and going south.
I had driven to the shop to buy the part intending to do it myself. But it would not start when I tried to leave. I sat in their parking lot waiting for the 30-60 minutes it usually took for the car to start. Was told by my tech to check for the engine RPM readout on VCDS (block 4 I think) when cranking. If the speed sensor was not bad the RPMs would show (200 to 400?) as the starter cranked and that meant I had another problem instead. If speed sensor was bad then there would not be a reading.
I never found out if this was true as when I set up to monitor the RPMs on VCDS and engaged the starter the RPMs showed and the car started. This was after sitting about 75 minutes with a no start. When it started I decided to have them replace the part. I was there and tired of the mess and did not feel like crawling under the car on 8" ramps when I got home. Glad I let them do it. It was not all that easy to access and was stubborn to remove.
Also interesting to note that only one time did I get a code about the G28 being intermittent. I reset it and continued to have problems with hot starts, no codes about the G28 came up again. Although replacing the CPS has resolved my problem.
I had driven to the shop to buy the part intending to do it myself. But it would not start when I tried to leave. I sat in their parking lot waiting for the 30-60 minutes it usually took for the car to start. Was told by my tech to check for the engine RPM readout on VCDS (block 4 I think) when cranking. If the speed sensor was not bad the RPMs would show (200 to 400?) as the starter cranked and that meant I had another problem instead. If speed sensor was bad then there would not be a reading.
I never found out if this was true as when I set up to monitor the RPMs on VCDS and engaged the starter the RPMs showed and the car started. This was after sitting about 75 minutes with a no start. When it started I decided to have them replace the part. I was there and tired of the mess and did not feel like crawling under the car on 8" ramps when I got home. Glad I let them do it. It was not all that easy to access and was stubborn to remove.
Also interesting to note that only one time did I get a code about the G28 being intermittent. I reset it and continued to have problems with hot starts, no codes about the G28 came up again. Although replacing the CPS has resolved my problem.
So you think it was your CPS (Crank Position Sensor) that solved your starting problem when the car was at operating temp? You mention "speed sensor" so I was just trying to clarify.
I recently changed out the CTS, but it didn't resolve my problem from the short time since. I did get my mechanic to hook up the car to VCDS and check again for any codes, but he said there was nothing and everything seemed to be okay. I told him about the hot start issue and told him I changed the CTS, so while it was still hooked up on VCDS he took a look and said the reading was 7-9% off which he said could be causing the starting issue. He asked if I used an OEM CTS replacement but I told him I just picked one up at the parts store to see if it would make a difference. He told me he has had problems before when he used anything other than an OEM CTS and given the reading he got on VCDS he said it still could be the issue. Now i just need to order a CTS and make sure it's an OEM, or go pick one up from the dealer. My mechanic said I could bring it back by and hook up again once I switched to see if that solved the issue. So hopefully later this week I'll be able to check.
10-30-2013, 05:43 AM
#29
AudiWorld Senior Member
So you think it was your CPS (Crank Position Sensor) that solved your starting problem when the car was at operating temp? You mention "speed sensor" so I was just trying to clarify.
Yes, I replaced the CPS and it solved my issue.
Yes, I replaced the CPS and it solved my issue.
10-30-2013, 09:20 AM
#30
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Thanks Clancy! I'm getting my OEM coolant temp sensor this week, so I'll see if that makes a difference. If not and I still don't get any codes, I may have to consider the CPS.