I was asked to look at this car for a slipping trans problem, and I wanted to run this past the members here for input.
I drove the car about 3 miles and in 1st and Reverse it feels normal, even on a steep hill, but once it shifts into a higher gear the trans slips and you can go only about 15mph.
It is shifting, because if you move the shifter into a lower gear while traveling…you can feel it downshift.
THere is a code of P0502 Vehicle speed sensor. and there is no Trans fluid visible thru the filler cap on the trans top.
Previously someone else worked on this car for the slipping trans…changed some sensors…but couldn’t fix the problem. THe owners don’t know what parts he replaced. He works for a Tire outfit and I’ve known him to lean towards used parts a lot.
The previous mechanic convinced them that it needs a new Cluster. I presume he means instrument cluster.
I have a feeling that he just threw parts at it hoping that something would stick.
I presume that he replaced the VSS, and it didn’t cure the problem.
Come to think of it…the code could be from before the other persons work. I should have cleared the code and test drove it again.
I’m looking at dropping the pan, replacing the filter, refill the fluid, and replace the VSS
My questions;
Could a instrument cluster have anything to do with the shifting problem.
Is the level of trans fluid supposed to be above the ledge under the filler cap, or is there a “full level” plug in the side of the trans.
If he replaced the VSS with a new one…and the fluid level is good…whats my next step.
Before I did anything I’d get the car in the air and check the fluid level.
Do you have a competent scan tool? I’d drive the car while watching transmission data, see what the car is commanding the transmission to do vs. what is actually happening. You can also watch your VSS and compare it to what the cluster is saying.
I’m gonna stick my neck out on this one since I’m no transmission expert. The VSS plays a big role in shift points along with the TPS & I believe the MAP sensor. If the transmission is receiving a command to shift at an excessively low point the clutch servos won’t get enough pressure to properly engage them and they will slip. I remember in the old days when shift points were controlled by TV linkage or cables. If they were adjusted too long the shift points would be too low and you would get slippage with your shifts because the transmission oil pump was turning too slow too provide enough pressure.
I agree with your plan of action. Also check the wiring and connectors for the VSS. Hopefully the slipping clutches haven’t burned the fluid,
I don’t believe so. Another comment: he may have been referring to the PLANETARY cluster. The chain shops love to tell you you need a planetary cluster then tell you you need a rebuild. Then they fix something simple (like the VSS) then charge you for a rebuild.
Thanks, everyone for the input.
I got the other mechanic’s number last night and am hoping to call him today to find out what he replaced.
My scanner is not capable of doing much more than reading codes, though it was pitched as doing so much more. Most vehicles it doesn’t even offer the KOER testing.
I guess I’m going to have to save up for a much better one in the future.
When I did inspect/ or look into the filler cap, for a fluid level…it didn’t smell like the fluid was burnt.
I’m planning on getting it on a car dolly and hauling it the 10 miles to my shop and getting it on the lift. Once I get the pan off and get a good look at the fluid and filter, I’ll have a better idea.
I figure $60 for a new filter and fluid change is a cheap test.
I talked to the Tire Mechanic today and he said that he was told by a GM Mechanic that he should replace the Instrument cluster. So he is dead set that it is the instrument cluster.
He said that the cluster has curcuits that tell the trans when it should shift, and because the spedo is not working…the cluster doesn’t know how fast the vehicle is traveling. I forgot to mention that the speedo isn’t working in my first post.He did replace the VSS with a new one , but never checked the fluid level or changed the filter and fluid. He feels that you would be throwing your money away on a filter and fluid, before you know the trans is ok. THat doesn’t make sense to me. How can you diagnose the trans without it having enough fluid.
I guess that my scanner does more than I thought. I was scanning a BMW for codes tyoday and found some features that I didn’t know the thing had. I always felt that the thing came with too little info on it’s use. I’ll have to take it over and maybe I can get more info on the car.
So I’m leaning on a filter and fluid change and see if it does us any good.
If the fluid were low enough (or bad enough) to cause problems it wouldn’t drive in drive or reverse but it does. You also mentioned it doesn’t smell burnt. I often smell the fill cap on these dipstickless transmissions like you did. The smell comes through quite strongly.
Speedometer is a high failure item on Cavaliers and many other GM’s. The dealer may fix it free. A new custer is about $300, the stepper motors go bad in them. They don’t control the tranny. You need a new mechanic.
I highly agree with you @Knfenimore; THe Tire Mechanic is their good friend and you know how hard it is sometimes to convince people that they need to take what he says with a grain of salt.
I was 98 percent sure that the speedo does not control the shifting and sends no input to the trans about vehicle speed. I have not gotten to go look at this car again and discuss the problem with the owners. I hope to stop out there today and get them to let me take the car to my shop, for a filter and fluid change.
This is a good example of why they should not have eliminated the dipstick in these cars. If I knew it needed two quarts, I’d add it and drive off with it to my shop to prove the point to them.
Maybe I should just bring out a couple of quarts of DEXIII and dump it in and see what the results are.
Here some schematics. As you can see on the first schematic the computer drives the speedo. The others show the different tranny controls. There is a VSS and an ISS Input Speed sensor located in the tranny… Here are some descriptions of the parts and how to test them.
Transmission Input Shaft Speed Sensor
The automatic transmission input shaft speed sensor (AT ISS) is a magnetic inductive pickup that relays information about the transmission input speed to the PCM. The PCM uses this information to control the line pressure, TCC apply and release, and the transmission shift patterns. This information is also used to calculate the appropriate operating gear ratios and TCC slippage.
The AT ISS mounts on the transmission case under the channel plate next to the drive sprocket. An air gap of 0.26 - 2.90 mm (0.010 - 0.114 inch) is maintained between the sensor and the teeth of the drive sprocket. The sensor consists of a permanent magnet surrounded by a coil of wire. As the drive sprocket is driven by the turbine shaft, an AC signal is induced in the AT ISS. Higher engine speeds induce a higher frequency and voltage measurement at the sensor.
Sensor resistance should be 625 - 725 ohms when measured at 20°C (68°F) . Output voltage will vary with speed from a minimum of 0.5 volts AC at 550 RPM, to 200 volts AC at 7000 RPM.
Vehicle Speed Sensor
The automatic transmission output (shaft) speed sensor (AT OSS) is a magnetic inductive pickup that relays information relative to vehicle speed to the PCM. Vehicle speed information is used by the PCM to control shift timing, line pressure, and TCC apply and release.
The AT OSS mounts in the case at the speed sensor rotor which is pressed onto the differential. An air gap of 0.27 - 1.57 mm (0.011 - 0.062 inch) is maintained between the sensor and the teeth on the speed sensor rotor. The sensor consists of a permanent magnet surrounded by a coil of wire. As the differential rotates, an AC signal is induced in the AT OSS. Higher vehicle speeds induce a higher frequency and voltage measurement at the sensor.
Sensor resistance should be 1500-1650 ohms when measured at 20°C (68°F) . Output voltage will vary with speed from a minimum of 0.5 volts AC at 25 RPM to 200 volts AC at 1728 RPM.