Can't accelerate after coasting downhill with truck in gear

dodge
ram1500

#1

While driving in Colorado’s beautiful mountains, my 2003 Dodge Ram 1500 will sometimes lose power and I cannot accelerate. The electronic throttle control indicator will come on. I will depress the accelerator pedal, but the engine doesn’t respond. The tachometer will show that the engine is idling at about 800 rpm. In order to correct the problem my solution has been to coast to the side of the road, shut off the engine and restart the engine. This only occurs after I have been going downhill with my foot off the accelerator but with the automatic transmission in gear.

I’ve tried to understand the ins and outs of the “drive by wire” system but can’t figure out what might be failing. Is it the throttle body itself? The 5.7L has an accelerator pedal position sensor, and a few other “normal” devices that feed into the electronic control loop: crankshaft position sensor, oxygen sensor, intake air temperature sensor, and a manifold absolute pressure sensor. The 5.7L doesn’t have a throttle position sensor (I guess that’s what the pedal position sensor does). I can’t understand what would cause any of this to fail after I have taken my foot off the accelerator for several seconds (how many seconds? I’m not sure) while going downhill.

Any help would be appreciated. This has been an intermittent problem for many years. The most recent occurrence included a slight noise that sounded like it was coming from the transmission. This has me very concerned. The first time it occurred the truck was in cruise control going up and down rolling hills outside of Amarillo, TX.


#2

There are several software updates to correct electronic throttle control problems on these trucks. First step is to read the fault codes stored in the system.

This is one old bulletin;

SUBJECT:
_ Flash: MIL and/or Engine Throttle Control (ETC) Light Illumination, Diagnostic Trouble Codes (DTCs), and/or Poor Idle Quality_
OVERVIEW:
_ This bulletin involves selectively erasing and reprogramming the Powertrain Control Module (PCM) with new software._

MODELS:
2003 (DR) Ram Truck

NOTE : THIS BULLETIN APPLIES TO VEHICLES EQUIPPED WITH A 5.7L ENGINE (SALES CODES EZA) BUILT ON OR BEFORE FEBRUARY 28, 2003.

SYMPTOM/CONDITION:
Vehicle operator may experience:
_ Poor idle quality._
_ Poor performance after starting the engine when the battery voltage is low._
_ Poor performance after extended closed-throttle downhill coast._
MIL and/or ETC light illumination.
Technicians may find the following DTC(s):
_ P2100 - ETC Circuit._
_ P2106 - ETC System - Forced Limited Power._
_ P2108 - ETC Module Performance._
_ P2112 - ETC - Unable To Open._
_ P2181 - Cooling System Performance_.


#3

Nevada,
Thank you for the cited bulletin.

According to KBB VIN lookup the vehicle was made June 20, 2003. Do these sorts of problems/solutions not apply since the bulletin says it’s for production prior to Feb 28, 2003?

CORRECTION: KBB did not give the date manufactured. I got that off of a report that was in my file. I don’t know if it is accurate or not.

Either way, I’m headed to get the codes. I hope they are still stored and available.


#4

So, I was able to get the the codes at O’Reilley’s. Codes 2106 and 2108 match the service bulletin. Those codes on the Bosch scanner come up as Throttle Actuator Control: Forced Limited Power and Module Performance. Those sound like my problem.

The man at O’Reilleys suggested going to the dealer. They want $145 to update the software but they won’t guarantee this will solve the problem. But the service guy says you should update your software regularly. I think I’ll see what a local mechanic recommends and charges tomorrow. But, since the service bulletin matches what I am experiencing, and I can’t understand how any of the sensors or the throttle control body should fail only under my circumstances I think I’ll try the software update. I bet the correction didn’t get performed on the date advertised in the service bulletin.

It’s a shame that the customers have to pay to fix a manufacturer’s software error.


#5

You can verify the trucks build date on the label in the left door jam, look for “MDH”, month, date, hour.

If you find a shop that subscribes to Tech Authority, the Chrysler service information site they will have access to the software revisions. Finding a shop that uses Tech Authority may be difficult.


#6

I’ve got a little roadblock on the door - it’s not original. But, by comparing the last six digits on the door jamb sticker to my vin it looks like my Dodge was built after April.

Thanks for your help. I’ll investigate the Tech Authority tip and see who I can find.


#7

Concur w/Nevada, if your vin number shows you need ecm software updates, and some of the updates are for the electronic throttle system, that’s the place to start. Especially if a visual check doesn’t show anything obviously wrong with the throttle actuator mechanism. It’s not all gunked up and looking icky, right?

If all that doesn’t pan out, putting on your thinking cap might work too. Think what happens when you go downhill with your foot off the gas and the transmission in gear? High intake manifold vacuum comes immediately to mind. If your engine uses a MAP device – that gadget is connected directly to the intake manifold by a thick hose — that could be failing due to the high vacuum. Depending on how it failed it could cause this maybe. And the throttle butterfly valve itself could be getting pulled down hard by the vacuum and sticking shut. That would be like if you have a door in your house that tends to stick in wet weather, but doesn’t if you only close it gently, don’t slam it shut. With high manifold vacuums that valve may be slammed shut with quite a bit of force, so it’s worth a consideration anyway. The throttle body would probably have to be removed for a look-see to check that. Nobody’s been messing with the mechanical stop on the butterfly valve, or poking screwdrivers to push on the butterfly, right?


#8

Update:
I decided to take a look at the throttle body today. It was gummed up a little on the upstream side at the edges of the throttle plate so I took it off and cleaned it. The backside was considerably dirtier. It’s hard for me to know if that is enough to be a problem of not. My plan is to take it on a mountain trip in a couple days and see if the problem recurs. I’ll post with those results.

George, I really like the idea of thinking through the problem. That’s why I started with the Service Manual. The only problem is I don’t have the knowledge/experience to arrive at the kind of possibility that you suggest with the manifold pressure idea. I basically don’t understand the things that are different when coasting down the highway versus normal driving conditions. So, I appreciate very much any ideas. Being ignorant sucks.

If the problem recurs I’ll get the software update even though it looks like the truck was built after the problem was corrected.

Also, no one has been messing with the throttle in any way. It just looked a little dirty - but it’s 13 years old so I don’t think it was unusually dirty.


#9

Here’s what it looked like before I cleaned it.



#10

From the photos it doesn’t look overly gunked up. It’s normal for the gunk to accumulate more on the downstream side. The PCV or EGR system is probably feeding in nearby, which can deposit some gunk up against the backside of the butterfly. I noticed that problem on my Corolla TB too.

With luck maybe you got it fixed, who knows. Let us know the results after your next test downhill drive.


#11

I made a trip in the mountains this morning. I’m not willing to claim success just yet, but thankfully it was uneventful. Tomorrow I plan to make another trip and will report on that as well.

Update:
2nd trip to mountains this morning with no issues. Problem solved with cleaning the throttle body??? I hope so. I’ll close this thread now with my thanks and wishes to all for a Merry Christmas and a Happy New Year!

Thank you especially George and Nevada!


#12

Sounds indeed like the throttle was sticking a little there. Good for you for cleaning the works & getting your 1500 back on the road in good operating condition!