05 suburban 5.3, keep getting "Reduced power mode"

[shady]

My kids 05 burb keeps going to reduced power. I don't remember the code, but when I googled it it came up as a Throttle position sensor issue was the usual culprit.

I have heard that trans slippage can cause that too. But his seems to shift great and shows no signs of slipping.

Is the TPS the right first step? Or are there a few other things I should check first?

 

[Blue85]

There are 3 main parts to the that system. The Throttle Actuator Control (TAC) module that decodes the Accelerator Pedal Position (APP) Sensor and runs the throttle body. The throttle body has the throttle motor and traditional TPS integrated to one package. Problem could be in any one of those three. I think there are some good troubleshooting guides floating around online to differentiate.

 

[shady]

I knew them three things have to work together. But haven't read anything about someone finding one of the others bad before lol. Hence why I asked here. I figured any one of them not working right could do it.
I wonder about it because it looks like maybe the TPS has already been changed. All the pics I seen of new ones it looks like they come with a new pigtail.
His truck has a new pigtail spliced in for the TPS.
Im not sure if they just did the wires, the TPS, or the whole throttle body.

Is the APP something that goes out on people. I know it's something that can. But I've never heard of some one having to change one.

 

[HankScorpio]

I have a medium duty that was having trouble with the reduced power mode. When I was researching it there are many different issues that will light up the reduced power icon. Its similar to running in open loop or "safe" mode, there is an issue not giving the ECU proper info. Many different codes can result in reduced power mode. If you have a code directing you to a specific component then I would start with that part and nearby wiring. Mine turned out to be wiring related.

 

[ZooMad75]

The app can fail. But I would not replace it without knowing what code set and follow the diagnostic chart for it. That could be a wiring issue. Pedals aren't cheap so throwing one on without testing would be a gamble.

One thing overlooked on the drive by wire systems is how clean in the actual throttle body and blade? A sticky throttle will cause codes to set. The system is looking for the throttle to move to the requested percentage in a certain amount of time. If it isn't moving quick enough because of a restriction like sticky buildup on the bore, the system assumes there is a problem and can force it into reduced power mode. So pop the intake snorkle off and check to see how dirty it is. They can get quite a bit of build up.

 

[shady]

The APP sensor is $68. I'm going to change the TPS and clean the throttle body this weekend. If it persists I'll change that APP next. It has 180k miles so some love in small doses can't hurt.

I REALLY hope it doesn't turn out to be wiring. Lol.

 

[ZooMad75]

If you like your fingers, clean the tb with the key off. Just saying.

 

[shady]

I was thinking clean it with the TB on a bench lol

 

[Blue85]

Don't you have some kind of scan tool? Watch the relevant signals while driving or datalog them to see if any of them is too slow, out of range, flat-spots, etc.

I think you can get a TPS by itself. You have to take the throttle unit apart and swap your old motor on, etc. It's not like the 90's where TPS was a stand-alone sensor. Don't know if those are available from any "good" brands.

 

[shady]

All I have is basically a code reader. It reads the code, tells you what the code is, and you Google Foo from there. I don't remember the actual code, but when I looked that up, 99% of the responses were about the TPS.
I already bought the TPS, and watched a couple videos about changing it. Been a while, so I'll have to watch em again. But it didn't seem too hard.

 

[shady]

This is the one I bought. It's dorman... But it's what I could get easy enough.

 

[shady]

The part that makes me wonder if it was ever changed is his is riveted on. All the aftermarket ones I've seen came with bolts or screws to re-install it

So maybe only the pig tail was changed

 

[Fordum]

Unless they have changed something while I wasn't looking, all that is, is a potentiometer. Easily tested with a cheap ohmmeter.
Actually, the cheaper the better. Just unplug the unit from the truck, and put the meter across two of the terminals. You want one probe on the wiper and the other on one or the other ends. Just pick two wires, put the meter across them and move the throttle.
If the needle moves, the wiper is on one of them.
A digital meter just will not show the results clearly. You need one with the needle. Just measure from the wiper wire to one side, and slowly move the throttle.
The needle should sweep smoothly across the scale.
Then, do the same from the wiper to the other side. Any jerkiness or dropouts means its bad.

Of course, since you have already bought it...........

 

[ZooMad75]

Unless they have changed something while I wasn't looking, all that is, is a potentiometer. Easily tested with a cheap ohmmeter.
Actually, the cheaper the better. Just unplug the unit from the truck, and put the meter across two of the terminals. You want one probe on the wiper and the other on one or the other ends. Just pick two wires, put the meter across them and move the throttle.
If the needle moves, the wiper is on one of them.
A digital meter just will not show the results clearly. You need one with the needle. Just measure from the wiper wire to one side, and slowly move the throttle.
The needle should sweep smoothly across the scale.
Then, do the same from the wiper to the other side. Any jerkiness or dropouts means its bad.

Of course, since you have already bought it...........

There's actually two position sensors on the throttle body for built in redundancy. They need to stay within a tight percentage as the throttle moves or the system assumes there is a problem and cuts power to the motor in the throttle body and the engine is in reduced power mode.

Ideally you would have to watch both tp1 and tp2 at the same time as it sweeps through the range from idle to wot. It can be done with a Tech2 scan tool or aftermarket scanner that can read data and not just codes. By going through a scan tool you are monitoring both circuits completely. Any change in resistance in the entire circuit is going to trip the same codes as if it was the sensor in the TB as all the system is watching is the change in voltage.

Just to give an idea of how tight the system is looking at the two sensor values if the difference between TP1 and TP2 is more than 6% for more than 0.14 of a second it will trip a correlation code like P2135. The system runs a test for that continuously as you drive.

 

[shady]

Well, that was dirty lol.
Its got a new Hitachi on it now.

 

[Fordum]

I figured something was up when I saw that a simple tps was almost $100. I am constantly amazed at the trend of auto engineers lately to totally screw up simple, solid and reliable systems that have worked for years.

I'm a tech guy, and I totally understand the almost overwhelming desire of other techs to monitor everything just because they can.
And the motto these days, when in doubt, throw a handful of CPUs in the mix.
And, I have personally done things like that. But only in personal equipment and would never do it in production equipment.
These folks need to understand the difference between a lab and the real world.
I keep running into stuff like this in my new Honda Passport. The other day, I was blasting down the highway, when I happened to look down at the voltage monitor I have plugged into the lighter socket.
It was reading battery voltage, at 70 mph. I checked my instruments, no alt or battery warning light. I figured I would check the voltage at the battery when I got home in a little while.
Glanced down a few minutes later, and it was reading 14.7.
10 minutes later, battery voltage again.
It was due for service a couple of weeks later, so when I took it in, I mentioned to the service manager that there seemed to be something wrong with the alt or voltage regulator.
He asked what it was doing, and when I explained, he said that was normal. The alternator voltage output is controlled by the computer now.
It uses an algorithm to cycle the alt on and off to improve gas mileage and supposedly increase battery life.
Which brings up another point folks here need to know about:
Computer controlled charging systems on these cars now, often change their charging strategies according to the age of the battery.
The idea is, as the battery ages, it needs different voltages or currents to prolong its life. So the computer does that.
Of course, the cynic in me wonders if the changes prolong its life, or are designed to kill it quicker after the battery warranty runs out.......

Nahhhh, they would not do that..........

Either way, if you do a simple job like replacing a worn out battery these days, you have to use a scan tool afterward to tell the computer the battery has been changed.
Otherwise, it will keep using the older battery charging plan and damage your new battery......

 

[shady]

Also, I'd like to reach out and F****n strangle whoever decided to run a coolant line through the TB for no apparent reason.

I pulled it off thinking it was a vacuum line, engine still hot, and sprayed my hands and face with hot coolant.

 

[Fordum]

They do that to preheat the air for better performance especially when the engine is warming up. Also, if you are ever flying above about 15,000 feet, it helps prevent carburetor icing.....

Of course, it has coolant under pressure when the engine is hot, so be sure to not take it off until the engine is cool......

BTW, seeing all that brown crud in the first pic, makes me think you might benefit from a catch-can. I am seriously considering putting one on my Ford. I get tired of cleaning the throttle body every few thousand miles so it will idle down.
They have really taken off due to the intake valve problems with the new direct injection gas engines, but it should stop the crud from building up in the throttle body also.

 

[shady]

seeing all that brown crud in the first pic, makes me think you might benefit from a catch-can. I am seriously considering putting one on my Ford. /QUOTE]
I thought of one of these already lol. Exactly what went through my mind

 

[Fordum]

If you put one on before I do, post something. I'll do the same. There are several of those out there, and I haven't made up my mind as to which one.
Plus, now that turkey season is over, the truck is going in the shop for some long overdue overhauls. Heater problems, oil changes, and I am finally going to get the winch back in operation.
The catch can may be part of all that.