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Mailbag: variety of DTCs and reduced engine power STS-V


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Hi Bruce I’m a big time reader of your STS V blog, have referenced it numerous times. I know you probably get this a lot but it’s hard to find people with knowledge on these Vs. I can get rid of this p0171 and 174 for the life of me. Car is also going into random reduced engine power mode, no rhyme or reason. So far, I’ve had intake filter, maf, crank position sensor, 02 sensors, and fuel filter all replaced. I’m starting to think this is an ecm issue
Can you point me in the right direction? Would love a phone call if you have time
Also getting p2135 p0651 5 volt reference which makes me think there is a short to the ecm
Reduced engine power message driving me nuts!! Please help.
 
hi; sorry I wasn't seeing this. What are all the current DTCs and I can start a thread on the forum so we get more eyes on the issue(s). What is the complete reduced engine power message?

Bruce

2016 Cadillac ATS-V gray/black

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p0651 b circuit, p0335 a circuit, p2135

 

had the cps, maf, bank 1 2 upstream changed, fuel filter, GM injector cleaning
p0171 sporadic
 
V0O5lxvn.jpg

Bruce

2016 Cadillac ATS-V gray/black

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The 5 volt code is worrisome.....but some other things to check.

Pretty sure that car is not using a throttle cable. But is a drive by wire. 

There are (2) throttle position sensors in the throttle body (TAC).....and one is in the gas pedal.

The p2135 code will put the car in 'reduced power mode' and send a display message to the IPC. 

 

Not sure if there is a repair for the throttle body TPS sensors.....you might have to replace the complete unit. 

 

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Ok thank you so much for the info. If I remember correctly, the tps sensors aren’t serviceable correct? And the TB can be replaced without taking the supercharger off? I know there’s minimal room back there

Is the accelerator position sensor near the gas peddle ?

yes I think the tb can be replaced without removing supercharger. but first would be to look at where the tps’s are wired to see if any have intermittant opens or fixable before throwing more parts at it

So I the wires that connect to the throttle body looked good to me and were getting the proper resistance and voltage when I probed them
 
Logan describes one tps as in the gas pedal
 
No breaks or cracks in the harness and outside tubing didn’t looks frayed on anything
 
Can I bench test tps? I have an extra supercharger just sitting here
 
with the car off you might try exercising the gas pedal through full movement multiple times to see if it is mechanically binding
 
8JwkuEoQ.jpg
 
not sure on tos test
 
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Bruce

2016 Cadillac ATS-V gray/black

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Thanks for the info the Bruce, I’ll update here. (Twitter DM)

ct5GFBRV.jpg

 

I-IECIFA.jpg

 

What threw me off was the 5 volt reference code
 
after the cps sensor was changed it came back
 
the cps code
 
yes may be unrelated unclear
 
Which makes me think the circuit to the ecm is throwing all sorts of codes
ok between work and army I can’t work on it and need my shop to get this done. But if they can’t figure out I’ll pop the hood myself and take another look
I’ll have them double triple check the tps sensor wires connectors
it would be good if they follow a diagnostic path to sort out what is wrong
 
Yeah they are a good shop. Just not happy about paying $1300 for the previous work and not fixing the issue
>>yes that gets old fast
You still have that beast of a sts v?
I spoke to the head Cadillac service guy at my local dealer, he said it could be even be a ground issue, which would drive me insane if it was that
I take what you suggested here and relay to my shop, diagnostic path to throttle body and accelerator position sensor
 

Bruce

2016 Cadillac ATS-V gray/black

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I think the shop created the lean code when they swapped the intake. Maybe a gasket rolled over or a hose may be unplugged. 

Just to be clear. There are (2) different TPS sensors in the throttle body. There is one in the the gas pedel. (3) total. 

Could be a ground issue or a rubbed thru wire. 

Stuff like the gas pedal sensor will 'look' brand new. What you really need is someone with a scan tool (and i dont mean autozone) that can look at what the sensors are doing voltage wise. 

Looks like the shop and the owner are just guessing at this point. 

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Original Author adds:
 
So I was getting those lean codes before any of this happened.. I usually can clear then by tightening clamps on cold air intake. But they remained even after the work they performed. I’m not sure on their scanners capabilities but yes I agree I’d like to get a definitive diagnosis.
I’ve seen multiple YouTube channels with the exact same codes, reduced engine power mode, and it ended up being one frayed wire
2KhH_hw1.jpg
This is the scanner they are using
Do advance GM scanners have the capability to literally connect into a sensor plug and see if there’s a break or short in one wire within the harness?

Bruce

2016 Cadillac ATS-V gray/black

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I responded:

GM Dealers use a custom scanner specific to their vehicles; it used to be called a Tech II as above now I think they have a computer interface for a laptop setup called MDI
otc-3846.gif
Is the mechanic you are at an actual Cadillac service facility?
 

Bruce

2016 Cadillac ATS-V gray/black

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Author wrote:

No they are a muscle car shop primarily but thought they had access to GM software, I could be wrong
 
that’s my next stop if this ecu flash doesn’t work, Cadillac service dealer

Bruce

2016 Cadillac ATS-V gray/black

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Just got off the phone with the shop, they said they will double check tps and pedal sensors, wiring, and run through the diag process. They are charging me for the ecm at cost flashed to the most recent GM software

Bruce

2016 Cadillac ATS-V gray/black

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Not sure why the PCM is being condemned at this point. 

"being one frayed wire"......yeap...all it takes is a very small nick or rubbing thru on a bracket to cause problems. 

The tool in the picture looks good enough. Knowing what you're looking at is more critical. 

 

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Owner Update:

So knock on wood. What I was suspecting from the beginning of this ordeal. The ECM. They swapped in a new ecm from the factory and is not pulling any codes after a 30 mile test drive. I told the shop to put at least 100 miles on it before returning to me. Will let you know the verdict tomorrow.

Bruce

2016 Cadillac ATS-V gray/black

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Owner update:

Spoke too soon. Car went into reduced engine power again, giving 5 volt reference on the other side now

 

Bruce

2016 Cadillac ATS-V gray/black

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That 5v reference code makes me think there is a pinched sensor wire somewhere. Just a hunch. I assume that was not there before all the work was done.

Very rarely is the ECM or PCM at fault. (On GMs...)

I highly recommend doing a thorough inspection of all what was touched. A harness may be improperly routed, pinched, etc...

There may be a loose hose or a cracked, mis seated gasket. A gasket that may be improperly installed. I realize this can make you nuts. Been there

GM FAN FOREVER

Nice, clean, luxury= fine automobile

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On 6/29/2021 at 6:48 PM, Bruce Nunnally said:
Hi Bruce I’m a big time reader of your STS V blog, have referenced it numerous times. I know you probably get this a lot but it’s hard to find people with knowledge on these Vs. I can get rid of this p0171 and 174 for the life of me. Car is also going into random reduced engine power mode, no rhyme or reason. So far, I’ve had intake filter, maf, crank position sensor, 02 sensors, and fuel filter all replaced. I’m starting to think this is an ecm issue
Can you point me in the right direction? Would love a phone call if you have time
Also getting p2135 p0651 5 volt reference which makes me think there is a short to the ecm
Reduced engine power message driving me nuts!! Please help.
 
hi; sorry I wasn't seeing this. What are all the current DTCs and I can start a thread on the forum so we get more eyes on the issue(s). What is the complete reduced engine power message?

Hi Bruce and others

I notice your in Plano, Tx

I just moved from Oregon to Greenville, Tx which is just east of you

I used to work for GM at the Tech center in Warren, Mi back in mid 1980s to early 1990s

Frankly you need to find a better dealer or shop as their diagnostics game plan is lacking

So just doing some thinking

1. PCM uses a 5 volt ref to several engin sensors such as CAM, Crank, TPS, APP, MAF, AIR, etc. So if the fuse for 5 volt (of PCM) or the PCM itself was faulty there would be a lot more problems and DTCs tripped so to me that leaves it is not a PCM issue

2. You did not mention if the engine goes into limp mode, if it does I would go right to diag APP (gas pedal and TPS) as 2 of your DTCs are drive by wire issues.  Depending on model year APP consists of 2 or 3 pots, the TAC (DBW controller) is doing multi checks to assure APP is not faulty and would cause a run away vehicle and cause a crash. Simply with a good OBD-II scanner (as I show below ) even with just key on, engine off APP and TPS can be seen if APP and TPS agree or not.

3. Also, can use the scanner to see if 5 volt ref is functional

4. Should be checking for TSBs for that vehicle as many times the problems are weak crimps of wiring pins or the wiring loom has no slack such as to APP and causes stress to wiring pins connections

As example :

SUBJECT:Service 

Update for Inventory and Customer Vehicles Main Engine Harness Wire Chafe Expires with Base Warranty

MODELS:2016 Cadillac ATS-V

This service update includes vehicles in dealer inventory and customer vehicles that return to the dealership for any reason. This bulletin will expire at the end of the involved vehicle's New Vehicle Limited Warranty period. 

PURPOSE

This bulletin provides a service procedure to inspect and, if necessary, reposition the main engine-wiring harness on certain2016 model year Cadillac ATS-V vehicles.

In some of these vehicles, the orientation of the main-engine wiring harness could cause the wires to contact and chafe against the right-front valve cover bolt and washer. If the engine-wiring harness insulation is compromised, the vehicle’s tachometer, powertrain, and automatic-braking systems could be effected. While this condition could—if uncorrected—cause a loss of propulsion or the activation of the automatic braking system, GM has no reports indicating that either event has occurred on a vehicle in the field.

This service procedure should be completed as soon as possible on involved vehicles currently in dealer inventory and customer vehicles that return to the dealer for any type of service during the New Vehicle Limited Warranty coverage period.

So check for other TSBs such as

VEHICLES INVOLVED 16 ATS-V TSBS

Check for how the DTCs are defined will help zoom into the areas to look at first such as :

 

Symptoms of a P2135 code can range from stalling when you come to a stop, total lack of power, no acceleration, sudden loss of power at cruise speeds or stuck throttle at current rpm.

Additionally, the check engine light will illuminate and the code will be set. Potential Causes of P2135 DTC It's been my experience that the wiring connector or "pig tail" on the throttle body gives problems in the form of a poor connection.The female terminals on the pigtail corrode or pull out of the connector.

Possible bare wire on pigtail shorting to ground.

The top cover on the throttle body distorted preventing the gears from turning properly. The electronic throttle body is faulty. The accelerator pedal sensor or its wiring failed.

The engine management computer has failed.

The TPS sensors were not correlating for a few seconds and the computer needs to be cycled through its relearn phase to restore active response to the throttle body, or the computer needs reprogramming at the dealer.

Diagnostic / Repair Steps A few points about the electronically controlled throttle.

This system is incredibly sensitive and vulnerable to damage, more than any other system. Handle it and its components with extreme care. One drop or rough handling and it's history. Apart from the accelerator pedal sensor, the remainder of the components is in the throttle body.

On inspection, you will notice a flat plastic cover on the top of the throttle body. This houses the gears to actuate the throttle plate.

The motor has a small metal gear protruding up through the housing under the cover. It drives a large "plastic" gear attached to the throttle plate.

The pin that centers and supports the gear fits into the throttle body housing and the top pin fits into the "thin" plastic cover.

If the cover is distorted in any way, the gear will be compromised requiring total replacement of the throttle body.

Pull the electrical connector out of the throttle body. Inspect it closely for missing or bent female terminals. Look for corrosion. Clean any corrosion using a small pocket screwdriver. Place a small amount of electrical grease on the terminals and reconnect it.

If the terminal connector has bent or missing pins you can pick up a new "pigtail" at most auto parts stores or from the dealer. Inspect the top cover on the throttle body for cracks or warping. If any are present, call the dealer and ask if they sell just the top cover.

If not, replace the throttle body. With a voltmeter, probe the accelerator pedal sensor. It will have 5 volts for reference and next to it a varying signal.

Turn the key on and slowly depress the pedal. The voltage should climb from .5 to 5.0 smoothly.

 Replace it if the voltage spikes or it has no voltage at the signal wire.

Look online for wire terminal identification on the throttle body of your vehicle. Probe the throttle body connector for power to the throttle motor.

Have a helper turn the key on and slightly depress the pedal. If no power is present, the computer is at fault. If there is power the throttle body is malfunctioning.

--------------------------------------

If problem is resolved, problems still might happen but it could be now that APP and TPS are NOT rezoned to PCM

Some GM makes to rezone TPS as to angle of TB butterfly is with key on, engine off, disconnect the wiring connector of TPS

PCM will trip a TPS DTC and set TPS angle at zero angle, go key off, plug TPS connector back in, turn key back on and PCM will rezone TPS angle to zero, Clear any DTCs

 

JR _ Team ZR-1 Corvette Racing - Custom GM PCM and TCM Tuning

 

app.jpg

Edited by teamzr1
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Thank you for the detailed response, and welcome to Texas & CaddyInfo.

I appreciate this may be confusing, but although yes I drive a 2016 ATS-V, this is a "mailbag" post which is to say someone emailed me directly instead of posting it in the forum.  That person has an STS-V, which is the vehicle with the issue; my ATS-V is fine.

I think your logic still applies for a good approach to diagnosis & I have also forwarded to vehicle owner.    Currently he is dealing with a muscle car shop, not a Cadillac dealer, and they were smoke testing the intake to try to establish why it is running lean 
DTC p0171 p0174 and the 5 volt reference

Bruce

2016 Cadillac ATS-V gray/black

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owner notes:

Oh I forgot to include some new information I have. The volt reference code is the OTHER side now, so no longer B circuit anymore but A circuit. Not sure how that happened after the new ecu or what it suggests

Bruce

2016 Cadillac ATS-V gray/black

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