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2008 CTS. engine light comes on, then service TCS. engine

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2008 CTS. engine light comes...
2008 CTS. engine light comes on, then service TCS. engine power is reduced. Will not allow the cruise control to work. limits carburetor and there has been times when it will keep the car from getting enough power to even move faster than 5 MPH. Last it can happen as I'm driving down the rd and it will cause the car to feel like I down shifted , and then no power. As you can tell the TC light with the accompanied Service TC system and reduced engine power is not all the time, but getting more an more frequent.
I had a serviceman tell me he thought it could be an electrical harness to the carb?
thoughts?
Submitted: 7 months ago.Category: Cadillac
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Answered in 5 minutes by:
6/12/2017
Cadillac Mechanic: Gunvir Singh,
 replied 7 months ago
Gunvir Singh
Category: Cadillac
Satisfied Customers: 1,878
Experience: Master Tech at Kennesaw Auto Tech
Verified

Hello, do you have the code for the check engine light?

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Customer reply replied 7 months ago
where would I get code?
Cadillac Mechanic: Gunvir Singh,
 replied 7 months ago

Do you have a code reader? If not, you can take it to an autozone for a free code reading.

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Customer reply replied 7 months ago
Great 1. i will take it to auto zone right now!
Cadillac Mechanic: Gunvir Singh,
 replied 7 months ago

Ok, let me know once you find the codes. then i will be able to help you better.

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Customer reply replied 7 months ago
P0606
P2138
Customer reply replied 7 months ago
Would this sensor effect the cruise control and traction control systems?
Cadillac Mechanic: Gunvir Singh,
 replied 7 months ago

Yes it can, let me get some info. PLease stand by.

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Cadillac Mechanic: Gunvir Singh,
 replied 7 months ago

P2138 is a faulty code that gets triggered due to a faulty Acceleration pedal position sensor, APP sensor wiring or pcm. P0606 is for a code for internal pcm error which can get triggered due to a faulty pcm.

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Customer reply replied 7 months ago
What is app sensor wiring, or pcm?
Cadillac Mechanic: Gunvir Singh,
 replied 7 months ago

App sensor is the acceleration position sensor which is built inside the accelerator pedal. PCM is the vehicle's computer that controls vehicle's electronics.

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Customer reply replied 7 months ago
where does the wiring go if I wanted to replace that?
I understand the pedal and sensor is a part that can be installed, but what about the wiring if that is bad?
Cadillac Mechanic: Gunvir Singh,
 replied 7 months ago

The wiring goes from the App sensor connector to the dash harness which goes to the pcm.

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Customer reply replied 7 months ago
Does the dash have to come off or how hard I'd it for a did project?
Cadillac Mechanic: Gunvir Singh,
 replied 7 months ago

The dash will not have to be removed. But you will need access to a scan tool and multimeter to perform a proper diagnostics.

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Customer reply replied 7 months ago
2008 CTs Cadillac engine light came on, now stays on. Traction control light comes on, and then service Traction Control system message with reduced engine power message. Previously intermittent. Now constant. I went to Auto Zone to get code read and it was P2138 and a general fault code for the ‘CPU” . Replaced the APP sensor last night. Started and no fault on the Traction control, but then on drive, it activated with message to service Traction Control system and reduced power. Engine light still on. If I shut the engine off the Traction control fault message with be eliminated but maybe 5-10 minutes later will come back on. At stop light this morning the car accelerated on its own. Felt like I had been hit from behind because my foot was still firmly on brake and it was like I was power-braking. Manually cleared engine light fault, new reading is the same as old; accelerator pedal position sensor 1-2 correlation. P2138
However new message also says ASE certified Master Technicians have seen this issue on your type of vehicle and the most likely solution is : repair Faulty wiring at Instrument panel.
1. What is the problem?
2. What is the solution?
3. What wiring at what instrument panel?
Last and perhaps not relevant: 18 moths had an ignition interlock devise installed, since removed. Problem may have started around the same time, but has persisted since removing the device.
Cadillac Mechanic: Gary, ASE Certified Technician replied 7 months ago
Gary
Gary, ASE Certified Technician
Category: Cadillac
Satisfied Customers: 1,383
Experience: Senior Technician
Verified

Hello James,

I have seen P2138 in many different GM vehicles.

Above 90% of those are a connector terminal issue.

I have replaced about 6 pedals, but about maybe 100 cars with wiring issues.

This is where is will get difficult for you.

To start with you need a GM scan tool for APP data display, a PCM wiring diagram, a multimeter, a breakout box if necessary, terminal test adaptors etc.

I would nearly bet on the interlock device installation and then removal as being the cause.

Lots of faults occur when accessories are fitted to cars.

Gary

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Customer reply replied 7 months ago
Thanks Gary. I'm looking at throttle body now. wiring to and from and Pin connectors to the ECM.
here is a new twist. Seems like when the engine is cool, ( new start) I have no TC message or reduced engine power. as an example I drive from a 77 degree garage this morning 5.5 miles and no TC light or reduced power.
Hmmmmm
does this help your differential diagnosis? My next plan is to check the ground wires, and then move on to the wiring, I thought I'd peek at the throttle body to see if it needed cleaning and / or jostle the wiring harness. Any suggestion would be appreciated.
James
Cadillac Mechanic: Gary, ASE Certified Technician replied 7 months ago

In most I know of, the APP wires go through a junction block where fretting corrosion occurs on the terminals. Some cars get a revised gold plated 6 pin connector to bypass the factory terminals. A good tech is needed for this job. I've done many.

The P2138 is a correlation code for a mismatch between the two APP sensor voltages.

One is always double of the other.

Eg. When APP1 is 1.74volts, AAP2 is 3.48volts.

When this doesn't happen, reduced performance is the default.

Your description sounds fairly typical of a high resistance connection, say 10 ohms instead of zero.

Gary

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Customer reply replied 7 months ago
on a 2008 Cadillac where would I find the APP junction box?
Customer reply replied 7 months ago
2008 CTS
Cadillac Mechanic: Gary, ASE Certified Technician replied 7 months ago

Hi James,

The wires for the APP would go through a large connector around 60-80 wires at the firewall.

But I can't locate a circuit or layout drawing for you, for your model.

If you look here you can see the connector in this example C104.

http://professional.justanswer.com/chat/index/f61aca8a6d8f45769772efa0bd677dfe

This is just an example of an intermediate connector. The throttle body is a short run, so has nothing in the middle.

Gary

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Cadillac Mechanic: Gary, ASE Certified Technician replied 7 months ago

Hi James,

You also had a P0606 which is a ECM internal fault.

Has a dealer tech looked at this fault?

Gary

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Customer reply replied 7 months ago
No. I have been doing this on my own.
I lost faith in my dealer /tech when they wanted to charge me over 1400 to replace a front bulb and rear bulb assembly. After they did the front I figured I'd buy the rear assembly from a salvage dealer because it is a uni body construction. So we just did the front and I went to my salvage dealer and lo and behold as I suspected ( but they denied) the rear fault was fixed by replacing the front bulb. So, had I authorized them it would have been an unnecessary expense of over $1000.
I cannot believe they did not know it at the time. I mentioned it to them the next time I was in for an oil change and they got pretty snippy with me so now I am DIY on anything I can.
I have a driver door sensor that is out too. I can use the fob to unlock all doors but have to key into the driver door.
I really don't trust the dealer tech anymore.
Cadillac Mechanic: Gary, ASE Certified Technician replied 7 months ago

Hi James,

Resources from the Internet might not be enough to help you isolate this wiring fault.

And almost as important is the intermittent P0606 which could be a power, ground, or internal fault of the PCM.

I used to have access to GM America, but unfortunately not now.

Would you like another expert's opinion if I opt out of your question?

Gary

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Gary
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Satisfied Customers: 1,383
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