Cross-Posting my Reduced Engine Power Thread - Need help!

[Mighty Hd]

Cross-Posting this as I need a bit more exposure to this ongoing saga. Any help is desperately appreciated, I am out of ideas other than a trip to the dealer at this point. :-(

Engine Power Is Reduced - Ongoing Issue, Updates throughout thread.

Vehicle is a 2013 Tahoe LT Z71 with 90k. Max towing pkg, two speed transfer case (2hi, 4hi, 4low & auto 4wd). Fuel pump failed and also the fuel pump control module. I swapped the fuel pump today and I’m waiting on the FPCM to arrive at the local dealer. I checked the modules and noticed there...

www.tahoeyukonforum.com

 

[BG1988]

i would check the throttle body and the wires & gas peddle REP code is tied into that..

when i disconnect the Throttle body power cable i get that message


one of the Thorrttle position sensors are acting funky bad bad wire, bad ground

in a OBD2 reader that has live data you can see if the throttle position % changes when the gas is pressed

one of the 5v lines might be grounded out or not functioning (it has 2 on the throttle "aka gas peddle" and two on the throttle body ) this is to prevent a malfunction engine run away condition.. or gas peddle issue when one of the resistors go bad from being worn out


see page 6 #28 here to diagnosis it

https://static.nhtsa.gov/odi/tsbs/2012/SB-10044229-8347.pdf

 

[Snowbound]

I’ve seen similar issues on a buddies ‘10 Tahoe. He was told by multiple shops it was the BCM causing his issues. Same thing, cleaned grounds, replaced battery, even did ground cable and issues would come and go. He changed the BCM and had it programmed and it ran great for a few days. Seemed like everything he did or shop did would make it run fine for a day or two and made him think it was fixed. Then go back to reduced power, limp mode. He was finally able to drop it off to me so I could do some testing. Ended up being a $25 termination resistor in the harness above the spare tire. I thought he was gonna kiss me when I told him I fixed it.

 

[Snowbound]

If I remember correctly he was having communication issues between modules and high and low voltage codes to different things. It’s been a while but that termination resistor is an important part for the LAN cables. There should be a resistance you can look up to confirm yours is bad but I think his read “I” for infinity meaning open. Be an easy test. It’s wrapped in tape to the harness above the spare. There are at least 2 in the system. But the rear one would be your issue if any I believe. Good luck and I hope this helps.

 

[Mighty Hd]

I have replaced:
MAP
Mass air flow sensor
Throttle body
Gas pedal
Fuel pressure sensor
Fuel pump (low pressure)
Negative battery cable
Positive battery cable mega fuse 170a
Fuel pump control module
Ground strap from the firewall to engine block
All 4 O2 sensors
All grounds have been cleaned and /or new terminal ends installed
- LT/RT front frame rails
- under driver door
- LT front dash near the pillar
- LT rear frame rail ground
- RT dash under the side cover

Wiring harness has been checked top to bottom.
I have a new ECM ..pending dealer scheduling to install.

I’m seriously ready to sell this POS. At 90k I shouldn’t be having these issues.

Just for the hell of it, I ordered the resistor posted above..

 

[Snowbound]

That’s one heck of a laundry list of parts to throw at it. Not being a smart guy here, but what I see missing from the post are things you’ve actually tested. Just the cost of parts alone would have been money better served taking it to someone who can do proper diagnosis. I sure hope that resistor fixes your problem just for your sanity. And it’s only $22.

 

[Mighty Hd]

Minus the cost of the ECM, I have around $350 in parts so not too bad. Between coupons and getting some of the parts at cost has helped.

 

[Mighty Hd]

Installed the resistor today.

Engine Power is reduced message does not appear with the factory tune installed.

The instant that I put on the blackbear tune, and even before I start the vehicle (key to ON) the EPR message appers.

I have a few messages into Justin @ Blackbear. I'll update the post when he replies

 

[BG1988]

Minus the cost of the ECM, I have around $350 in parts so not too bad. Between coupons and getting some of the parts at cost has helped.

the GAS peddle it self will throw the REP code CHECK with the OBD2 reader to confirm it's funtional

 

[Mighty Hd]

the GAS peddle it self will throw the REP code

The gas pedal was replaced as well early on...

 

[BG1988]

The gas pedal was replaced as well early on...

CHECK with the OBD2 reader to confirm it's functional and reading correctly

 

[BG1988]

Look for Accelerator pedal position D and E sensors on OBDII live data

(APP_D (%)
APP_E (%)
TP_R(%)
TP_B(%)
TAC_PCT %

Inside your Accelerator Pedal Position Sensor, you actually have two or more separate sensors which the ECU uses to validate the integrity of the signals. These both are fed two different voltage sources (one sensor (sensor E) gets half the input voltage compared to D, causing half the output voltage) by the ECU as a fail-safe.


If they're are NOT moving you have a wire fault or bad ECU if you all ready replaced them

at that point each wire will need to be conductivity tested to the ECU

you checked for transmission codes ? Catalytic Converter clogged?
o2 sensors working?

​

 

[Mighty Hd]

Here is a link to all of the data for the throttle actuator. I think this is what you’re looking for? Everything looks good

https://imgur.com/a/vekQUV3

How’s this little gem for some laughs.

 

[BG1988]

Here is a link to all of the data for the throttle actuator. I think this is what you’re looking for? Everything looks good

https://imgur.com/a/vekQUV3

We found the ISSUE!
it should be at 15-19% idle (may vary per the idle rpm set at the factory)
a value of 0% means it's not working..


idle it shows a percentage on mine

[idle] APP_D 19.2% & APP_E 9.4% (May vary because of factory set idle speed)
[Full Throttle] APP_D 85.1% APP_E 42.4

even in autostop the gas peddle will still read something

 

[Mighty Hd]

Can anyone else confirm?

I did a relearn and a throttle sweep relearn and I’m still getting the same results.

I noticed yours is a hybrid

Checked the wiring/plugs. Everything looks ok.

 

[BG1988]

Can anyone else confirm?

I did a relearn and a throttle sweep relearn and I’m still getting the same results.

I noticed yours is a hybrid

Checked the wiring/plugs. Everything looks ok.

you did a resistance check
look for an open wire

the gas peddle is identical

 

[Mighty Hd]

How does this come into play when this only occurs under these conditions

- vehicle is driven and warmed up
- hot soak for 10+ minutes
- ONLY with the Blackbear tune. It does not occur with the factory tune. I have extensively verified this.


Grrrrr... Quite frustrating.

 

[Mighty Hd]

No response from Blackbear as of my last messages 2? Weeks ago and data logs. They must be backed up.

EFI / HPtuners forums seem to agree there is a calibration issue with the tune and the throttle body as others have had the same issue in the past.