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Discussion Starter #1
Hey guys. So my 2008 Acadia has occasionally been throwing my traction light on with a couple dings, and then my DIC says "Traction Control Off", "Service Traction Control", Service Stabilitrak", since November 2015. I just had my transmission valve body replaced in November and this problem has now been doing this ever since. Well it will only throw this while I'm driving but my engine power does not reduce. The light just comes on and that's it. Now February 2016, it was doing this and on the way home my brake lights were staying on while I was driving. They would not shut off until I shut the car off. Hopefully its a sensor issue. Any ideas? TIA.
 

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There is a DTC set. If there is no check engine light then it is a chassis trouble code that is set (ie. CXXXX, not PXXXX). You need better software to read chassis codes (and body codes, BXXXX). These display messages are telling you that EBCM (electronic brake control module) has discovered a fault. The system is quite complex as the EBCM controls a variety of things, including ABS, motor mount dampening, traction control, and steering wheel effort.

Finding out what this code is will save you from guessing. If you still want to diagnose a wheel speed sensor, here is the proper procedure:
To test for the "12 volt Wheel Speed Sensor Supply Voltage" from the EBCM with a WSS fault present, perform the following test:
•  Disconnect the Tech 2 and Key Off Ignition, Remove Key, Open and Close the drivers door to turn off RAP (Retained Accessory Power) and wait at least 60 seconds.
•  Disconnect the appropriate WSS harness connector.
•  Connect a Fluke 87 DVOM (J39200) across the wheel speed sensor "Supply Voltage" and "Signal" circuits from the EBCM.
•  Set the DVOM on DC volts, press the "range" button to the 40 or 60 volt scale and then press the Min/Max button.
•  Turn the ignition key on. There will be a quick momentary 12 volt pulse from the EBCM at key up. This 12 volt pulse is sent each time the EBCM is powered up after being asleep to check the WSS circuit integrity.
•  If the 12 volt pulse is present continue with the WSS component testing. If the 12 volt pulse is NOT present recheck the circuits between the EBCM and WSS before replacing the EBCM. Make sure there are no backed out or loose terminals at the EBCM, WSS, or any inline connectors using the appropriate Terminal Test Probe.

Component Testing of the Wheel Speed Sensor
•  Ignition OFF, disconnect the harness connector at the suspect wheel speed sensor.
•  Connect a 3A fused jumper wire between Battery B+ and the "12 volt High Wheel Speed Sensor Supply Voltage" terminal.
•  Connect a Fluke 87 DVOM (J-39200) in series between the Battery Ground and the "Wheel Speed Sensor Low Signal Return" terminal.
•  Set the DVOM to the DC Milliamp scale.
•  The typical reading will be 4 to 8 mA for the "Low" reading and 11 to 16 mA for the "High" reading. As the wheel is turned very slow, a few degrees at a time, the signal will change from the low to the high reading as each reluctor tooth passes the WSS. 
•  If not within the specified range, replace the wheel speed sensor.
EDIT: Now that you've added more details, it is highly unlikely a WSS issue, but I'll leave the procedure there for future readers. Why didn't you take it back to the shop that did the work? What makes this more interesting is that the stop/brake lamps are controlled by the BCM (body control module), not EBCM. So, it should be easier to diagnose. The stop lamps staying on say that it could be an issue with the brake pedal position sensor or brake pressure sensor. I bet you have a C0277 or C0161 or something similar. If you can get the code read, I can help you with the diagnosis, but I cannot give you a definite solution without more info.
 

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(confused as to whether the OP is talking about the brake light in the dash, or the outside stop lamps) :shrug:
 

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Speleos said:
(confused as to whether the OP is talking about the brake light in the dash, or the outside stop lamps) :shrug:
Hmmm... Good point. I ran with the idea of it being the exterior lamps.
 

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Discussion Starter #7
So after taking the acadia to the mechanic they informed me that it is a stop light switch -- which I'm guessing is the same as a brake light switch. But I'm not sure if thats the same thing as the brake pedal positioning sensor. I'm not very familiar with all the lingo and part names. But they will fix it tomorrow for $115. Mechanic said that when he was test driving the car that the light came on with the messages on the DIC. So I'm guessing they ran a scan on it but he never said if he did or didn't. So I have no idea what codes were thrown out of it. So hoping it will be fixed and I will be done with this issue. At least they said it wasn't a major problem. :thumb:
 

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amyslim said:
So after taking the acadia to the mechanic they informed me that it is a stop light switch -- which I'm guessing is the same as a brake light switch. But I'm not sure if thats the same thing as the brake pedal positioning sensor. I'm not very familiar with all the lingo and part names. But they will fix it tomorrow for $115. Mechanic said that when he was test driving the car that the light came on with the messages on the DIC. So I'm guessing they ran a scan on it but he never said if he did or didn't. So I have no idea what codes were thrown out of it. So hoping it will be fixed and I will be done with this issue. At least they said it wasn't a major problem. :thumb:
Ask him for the exact chassis trouble code.

I can't believe you will pay someone to fix you car without confirming a proper diagnosis. I told you the part name above (brake pedal position sensor), and even guessed the same diagnosis without even looking at your car. He could be playing the guessing game as well. If he does replace the part make sure he does the calibration that is required after replacement.
 

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Discussion Starter #9
I will ask him tomorrow when he picks the car up. And to clarify...I didn't actually speak to him. I'm just going by what the invoice says that was left in my car. So I will ask him tomorrow.
 

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Discussion Starter #10
And we live in a small community where everybody knows everybody. So if there is a problem and it gets around it will for sure hurt their business so they try their best to make sure that they appease everyone's needs. It's not like I live in a major city. LOL. I live where most of the vehicles you see on the roads are farm equipment.
 

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amyslim said:
So after taking the acadia to the mechanic they informed me that it is a stop light switch -- which I'm guessing is the same as a brake light switch. But I'm not sure if thats the same thing as the brake pedal positioning sensor. I'm not very familiar with all the lingo and part names. But they will fix it tomorrow for $115. Mechanic said that when he was test driving the car that the light came on with the messages on the DIC. So I'm guessing they ran a scan on it but he never said if he did or didn't. So I have no idea what codes were thrown out of it. So hoping it will be fixed and I will be done with this issue. At least they said it wasn't a major problem. :thumb:
I've replaced 4-5 of these on our Outlook - yes that many. They seem to die about every 9-12 months on us. Luckily, it is a sub $20 part on Amazon and you can do it yourself next time in 5 minutes. Right under dash above brake pedal.

http://www.amazon.com/gp/product/B007QB7XYW?psc=1&redirect=true&ref_=oh_aui_search_detailpage
 

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vwtodd said:
I've replaced 4-5 of these on our Outlook - yes that many. They seem to die about every 9-12 months on us. Luckily, it is a sub $20 part on Amazon and you can do it yourself next time in 5 minutes. Right under dash above brake pedal.

http://www.amazon.com/gp/product/B007QB7XYW?psc=1&redirect=true&ref_=oh_aui_search_detailpage
I feel like I'm not that qualified or talented to handle that. ;D And my husband prolly could but he's working swing shift so finding the time is getting difficult.
 

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vwtodd said:
I've replaced 4-5 of these on our Outlook - yes that many. They seem to die about every 9-12 months on us. Luckily, it is a sub $20 part on Amazon and you can do it yourself next time in 5 minutes. Right under dash above brake pedal.
Do you make a habit of driving with your left foot on the brake pedal?
 

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lamping.ap said:
How do you know they died and just didn't need calibrated?
Nothing to calibrate. Cheap, sealed plastic part. My guess is that the metal contacts inside that measure resistance are flimsy and simply wear out.
 

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amyslim said:
I feel like I'm not that qualified or talented to handle that. ;D And my husband prolly could but he's working swing shift so finding the time is getting difficult.
It is literally 5 minutes total once you do it.
1. Remove plastic panel under dash by pulling 4-5 push clips.
2. Unclip harness from sensor.
3 One small screw with hex head - use small adjustable wrench, socket, or nutdriver. Socket easiest due to space.
4. Plug in harness and replace panel - done!
 

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Speleos said:
Do you make a habit of driving with your left foot on the brake pedal?
Not at all, however, there is a slight bit of lateral play in the pedal by nature of its mounting under there and I can only guess that the slight sideways movement every time you press the pedal eventually wears the sensor.

When this switch goes out, you lose brake lights (or they stick on), the transmission shift lockout in park won't release when you push the pedal, and the ABS/TC/Stabilitrack are all deactivated. All for one little $16 part.
 

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vwtodd said:
Nothing to calibrate. Cheap, sealed plastic part. My guess is that the metal contacts inside that measure resistance are flimsy and simply wear out.
100% false. The BCM needs calibrated to parameters of the new sensor.

From the FSM:
Brake pedal position sensor calibration must be performed after the brake pedal position sensor or body control module (BCM) have been serviced. The calibration procedure will set the brake pedal position sensor home value. This value is used by the BCM to determine the action of the driver applying the brake system and to provide this information to the vehicle subsystems via the GMLAN communication bus.
The EBCM disables the TC and Stabilitrak because it is being told the brakes are being applied and the car is accelerating at the same time. It decides that it cannot trust the inputs it is receiving, and disables the systems and sets a chassis trouble code. Reading the chassis code would give you a better idea of the exact issue, but I guess some people prefer to guess and spend money repeatedly replacing parts.
 

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vwtodd said:
Not at all, however, there is a slight bit of lateral play in the pedal by nature of its mounting under there and I can only guess that the slight sideways movement every time you press the pedal eventually wears the sensor.
Either something in your driving habit, or lack of attention to change-out procedure is causing the repeated failure. You're one of very, very few (if not the only one here) who experiences this trouble repeatedly.
 

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lamping.ap said:
100% false. The BCM needs calibrated to parameters of the new sensor.

From the FSM:
The EBCM disables the TC and Stabilitrak because it is being told the brakes are being applied and the car is accelerating at the same time. It decides that it cannot trust the inputs it is receiving, and disables the systems and sets a chassis trouble code. Reading the chassis code would give you a better idea of the exact issue, but I guess some people prefer to guess and spend money repeatedly replacing parts.
"100% false" or not, All I know is that I have had 4-5 of these go bad, and all I do is replace them myself - in 5 minutes - recycle the ignition (which may re-calibrate the system with new switch in place - don't know) and it works perfectly for 9 months to well over a year.

For what I was charged the first time - around $170 for the "diagnostic fee" to look at the light, then overcharged for the part - I can replace this *another* 5 times and still break even on what it would cost to take it back to the dealer for one similar repair.

The dealer installed the first one and it failed - are they doing it incorrectly as well??
 
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