CoolAirVw
Vendor
01m part 1
I’ve been asked to share some info on auto trans diagnosis. I’ve been collecting pictures and data from a few cars that I’ve worked on and I thought I would share the info in this thread.
Edit 4-3-21 Made a video regarding diagnosis on g68 sensor and since this thread is about speed sensors I though I would post a link here.
EDIT: 11-29-18. Made a 01m diagnosis video and didn't want to start a whole thread about it so I decided to place it here. It related to fluctuating, erratic speedometer, and repair process. This is not a how to repair video. Maybe I'll make one as my car has this problem also. If you want a how to video please post in the comments of the video.
This customer’s first call to us was asking, “How much for a transmission on my Bug.” He thought he needed his trans rebuilt or replaced.
Victim…99 Bug 01M
Mileage: 117,000
Complaint…High gear starts
First step in Diagnosis is scan for codes. Some might say first step is checking fluid. I wouldn’t argue, except that you have to lift the car to check fluid, which is a hassle, and you need a scanner to read temp, so why not check codes first?
Here’s the Codes we got…..
00281 vehicle speed sensor (g68) no signal
00297 vehicle speed sensor (g38) no signal
Volkswagens terms are confusing, so I’ll clarify. I don’t like the way VW calls 3 sensors on the trans “Vehicle Speed Sensor”. At least they name them, g68, g38 or g22.
G38 senses the speed of the sun gear shell inside the trans. It’s in the “middle” of the trans right next to the cooler. For a simple understanding of how it is used, just remember that the sun gear shell is stopped for 2nd and 4th and the speed with which it stops and starts, as the shifts, helps the computer determine apply rate of the clutches. In other words it uses this sensor to help control shift feel.
G68 senses the speed of the output of the trans. This is the one under the trans mount with a long harness on it. Obviously, with a transmission that is computer controlled, the computer needs to know what speed the car is going to make up shifting and down shifting decisions. It also compares this sensors signal with engine rpm to determine if the trans is making the correct gear ratio, or if the TCC is slipping.
G22 is on top of the differential section of the transmission and is used for instrument cluster signal, which is what I would normally call a vehicle speed sensor. This sensor doesn't input to the transmission computer and has no bearing on how the transmission works.
Back to the diagnosis…
A quick ohm check of the harness showed that the g38 and g68 sensors were “open”. Ohm checks are good for diagnosing hard problems but if the sensors were “going open” or “shorting” intermittently, then a ohm check is inconclusive.
So we order up a pair of sensors. Wait 3 days. Then we pull the g68 and see this….
No wonder the sensor was open! G38 looked the same, and this is what we saw in its hole. Broken off copper windings..
Both g68 and the g38 looked like this.
“Oh, no!”, I thought! The only logical conclusion is that the shafts are spinning “out of round” and beating the crap out of the sensors! About this time I start thinking, “Lets put in a 5 speed!” (just kidding!)
Well I already had the new sensors…
So, I stuck the g68 in the hole and rolled the car, then pulled the sensor back out, to see if it would “scrape up” the new sensor. It didn’t, so I bolted it up and rolled the car, pulled the sensor out again, and it still didn’t scrape up the sensor. Then I tried driving it. Then I put in the g38.
After clearing the codes and the trans working good, I re-inspected again and the sensors showed no sign of contacting the internal parts.
Edit: 5-15-17
I'm putting this info here because this thread relates to speed sensors. Quite frequently folks might hypothesize that the trans computer might be causing their issue if they replace a 01 speed sensor and the problem is still present. If you put a new g68 sensor in, and the problem isn't solved, then read the following thread where I walked a sharp guy through diagnosis this type of problem. .
http://forums.tdiclub.com/showthread.php?t=477187
To summarize, there should be about 2.5 volts on the sensor wires. This is a "reference voltage" that the computer puts on the sensor wires and the sensor signal "rides" on that voltage. If this voltage is missing then you could have a failed TCM. You can see this voltage in vagcom in the measuring blocks labeled g68 voltage. It should say about 2.5v. Please don't contact me and ask if 2.4v is close enough. If it doesn't show 2.5v and the sensor has been replaced then break out the voltmeter and see if there are 2.5 v on the wires at the sensor and if there isn't then pull the TCM and backprobe the sensor wires and see if there is 2.5v there. If there is not then most likely you need a TCM. I have a selection of TCMs if you need them.
Note: if the sensor fails it will not show 2.5V on vagcom. The above paragraph only calls for a new TCM if there is not 2.5V and the sensor has been replaced and there is not broken wires to the sensor. .
But this isn’t the end of the story…
Of course we knew we didn’t get all the material out of the trans. So we pulled the pan to inspect.
If someone saw this without knowing the sensors were destroyed, which they wouldn’t if they didn’t scan it, then they would think, “that’s a lot of metal, that trans is failing, we better stick in a 5 speed.”
This design of filter is good at trapping contaminants, so we broke it open!
Once again, if you didn’t know the sensors were shredded, then you would think this trans had some major failure!
continued in next post...
I’ve been asked to share some info on auto trans diagnosis. I’ve been collecting pictures and data from a few cars that I’ve worked on and I thought I would share the info in this thread.
Edit 4-3-21 Made a video regarding diagnosis on g68 sensor and since this thread is about speed sensors I though I would post a link here.
EDIT: 11-29-18. Made a 01m diagnosis video and didn't want to start a whole thread about it so I decided to place it here. It related to fluctuating, erratic speedometer, and repair process. This is not a how to repair video. Maybe I'll make one as my car has this problem also. If you want a how to video please post in the comments of the video.
This customer’s first call to us was asking, “How much for a transmission on my Bug.” He thought he needed his trans rebuilt or replaced.
Victim…99 Bug 01M
Mileage: 117,000
Complaint…High gear starts
First step in Diagnosis is scan for codes. Some might say first step is checking fluid. I wouldn’t argue, except that you have to lift the car to check fluid, which is a hassle, and you need a scanner to read temp, so why not check codes first?
Here’s the Codes we got…..
00281 vehicle speed sensor (g68) no signal
00297 vehicle speed sensor (g38) no signal
Volkswagens terms are confusing, so I’ll clarify. I don’t like the way VW calls 3 sensors on the trans “Vehicle Speed Sensor”. At least they name them, g68, g38 or g22.
G38 senses the speed of the sun gear shell inside the trans. It’s in the “middle” of the trans right next to the cooler. For a simple understanding of how it is used, just remember that the sun gear shell is stopped for 2nd and 4th and the speed with which it stops and starts, as the shifts, helps the computer determine apply rate of the clutches. In other words it uses this sensor to help control shift feel.
G68 senses the speed of the output of the trans. This is the one under the trans mount with a long harness on it. Obviously, with a transmission that is computer controlled, the computer needs to know what speed the car is going to make up shifting and down shifting decisions. It also compares this sensors signal with engine rpm to determine if the trans is making the correct gear ratio, or if the TCC is slipping.
G22 is on top of the differential section of the transmission and is used for instrument cluster signal, which is what I would normally call a vehicle speed sensor. This sensor doesn't input to the transmission computer and has no bearing on how the transmission works.
Back to the diagnosis…
A quick ohm check of the harness showed that the g38 and g68 sensors were “open”. Ohm checks are good for diagnosing hard problems but if the sensors were “going open” or “shorting” intermittently, then a ohm check is inconclusive.
So we order up a pair of sensors. Wait 3 days. Then we pull the g68 and see this….
No wonder the sensor was open! G38 looked the same, and this is what we saw in its hole. Broken off copper windings..
Both g68 and the g38 looked like this.
“Oh, no!”, I thought! The only logical conclusion is that the shafts are spinning “out of round” and beating the crap out of the sensors! About this time I start thinking, “Lets put in a 5 speed!” (just kidding!)
Well I already had the new sensors…
So, I stuck the g68 in the hole and rolled the car, then pulled the sensor back out, to see if it would “scrape up” the new sensor. It didn’t, so I bolted it up and rolled the car, pulled the sensor out again, and it still didn’t scrape up the sensor. Then I tried driving it. Then I put in the g38.
After clearing the codes and the trans working good, I re-inspected again and the sensors showed no sign of contacting the internal parts.
Edit: 5-15-17
I'm putting this info here because this thread relates to speed sensors. Quite frequently folks might hypothesize that the trans computer might be causing their issue if they replace a 01 speed sensor and the problem is still present. If you put a new g68 sensor in, and the problem isn't solved, then read the following thread where I walked a sharp guy through diagnosis this type of problem. .
http://forums.tdiclub.com/showthread.php?t=477187
To summarize, there should be about 2.5 volts on the sensor wires. This is a "reference voltage" that the computer puts on the sensor wires and the sensor signal "rides" on that voltage. If this voltage is missing then you could have a failed TCM. You can see this voltage in vagcom in the measuring blocks labeled g68 voltage. It should say about 2.5v. Please don't contact me and ask if 2.4v is close enough. If it doesn't show 2.5v and the sensor has been replaced then break out the voltmeter and see if there are 2.5 v on the wires at the sensor and if there isn't then pull the TCM and backprobe the sensor wires and see if there is 2.5v there. If there is not then most likely you need a TCM. I have a selection of TCMs if you need them.
Note: if the sensor fails it will not show 2.5V on vagcom. The above paragraph only calls for a new TCM if there is not 2.5V and the sensor has been replaced and there is not broken wires to the sensor. .
But this isn’t the end of the story…
Of course we knew we didn’t get all the material out of the trans. So we pulled the pan to inspect.
If someone saw this without knowing the sensors were destroyed, which they wouldn’t if they didn’t scan it, then they would think, “that’s a lot of metal, that trans is failing, we better stick in a 5 speed.”
This design of filter is good at trapping contaminants, so we broke it open!
Once again, if you didn’t know the sensors were shredded, then you would think this trans had some major failure!
continued in next post...
Last edited: