Truck isn't running over 40 MPH - please advise
 

Hey everyone. I'm having a major problem here.

My truck is out on the road with a friend and he said it won't go past 40 mph, but the speedometer is reading 80mph. He is reading his actual speed from the GPS unit.

I had him go to the nearest Autozone to pull the code and it comes up with a P0540, which to me shouldn't cause the truck to run like this. Am I right? The SES light is not even on at the moment.

Does anyone have any idea what is going on or what he could do to get back on the road? He is 700 miles from home and driving 40 mph isn't going to be fun. I also don't want him to mess anything up by driving it any further if he can help it. However, I really need the truck to get back to me and can't really afford to have it fixed while he is gone.

You guys would really be saving my ass by helping me out here. I'll be checking back every few minutes! Any help at all would be appreciated. Thanks.

sounds like the trans to me. if the speedo is reading 80 when only doin 40 something is sliping somewhere unless you have been having problems with the speed before this. if it was in limp mode the SES light would be on and the motor would govern out at 2000 rpms

He said everything seems to be running fine other than being governed to 40. It started up this morning and as he pulled onto the interstate, he couldn't get any faster than 40.

There haven't been any problems with the truck or transmission. The only issues with this truck have been the injectors which it eats like cereal, but the problems don't seem indicative of injector failure. I could be wrong.

Is there any way to test the transmission? It's an automatic.

Thank you for the reply. :tu:

well it should shift 4 times as your accelerating :w2: Do the rpms govern out?? It also could be the fuel filter if your lacking power.

if its the tranny the rpm will sky rocket and not move anywhere if its pulling strong then its not the tranny

I spoke with him and he confirmed the shifting was normal. The truck shifts up until it hits 40 mph and then just feels governed. He didn't count how many times it shifted, but he feels confident it shifted at least 4 times before the speed topped out. The rpms sit at about 2700 while driving at 40mph and do not govern out at 2000.

Also, the speedometer actually isn't stuck at 80, it somewhat mirrors the actual speed but at about 2x higher. When he is going 20, the speedometer reads about 40-45.

EDIT: He is currently pulling a 40ft trailer and has no noticeable lack of power.

2700 rpms at 40 mph would be like second or third gear

Hmm.. I'll tell him to pull over and count the gears as he accelerates.

Thanks so far guys. What a nightmare. :ouch:

EDIT: He counted and he is in third gear, but if he keeps pushing on the pedal the truck kicks into 4th gear likes it's in passing gear, but then downshifts again once it gets going.

Ditto the last post. 2700 RPM at 40 mph is way out of wack if the transmission is in overdrive...not possible really. Sounds like the tranny is not shifting to the upper ranges.

no tranny codes

I don't know how to pull the codes. I had him go to an Autozone to pull the ECM codes and the P0450 code is the only one there was. Are they stored in a separate area?

EDIT: I don't see any way to pull tranny codes without taking it to a shop (from searching online) and having them hook it up. Sorry I can't provide those.

tranny fluid level? condition of fluid, does it smell burnt or black in color?:humm:

I will have him pull over and check.

Thank you.

EDIT: He is pulling over for fuel in a couple minutes and will check the fluid then.

On a side note, he said while accelerating, the rpms hit 3000, shift to 2nd, up to 3000, shift to 3rd, then hit 2700 rpms and stay right at 40mph.

im not a dmax expert by any means but i hear that these trucks can go into "fuel limp mode" which means a dirty fuel filter and a new one fixes the problem<<<correct me if im wrong

He checked the tranny fluid and said that it looks nice and clean.

This truck just had a new fuel filter put on about 4000 miles ago. Could it be that dirty already? Also, there is no SES light on right now to indicate it is in limp mode. I've had it go into limp mode before when the injectors went out and the SES stayed on. Can it go into limp mode without the SES light on?

:humm:

ive got a cummins but from the way it sounds it seems like a possibility of a clogged fuel filter...almost dead pedal at 40 mph...

Thank you for the suggestions and help so far.

Since there doesn't seem to be anything we can do (from the feedback so far), I told him to go ahead and try to make it home. I'll be crossing my fingers.

this is a stupid question. Did he accidently put it in 4 low? you should change your fuel filter every 5 - 7 thousand miles. If it was in limp mode because of the fuel filter it would govern out at 2000 rpms. If it goes into trans limp mode the trans would lock its self in 4th gear and you would have no reverse. Did he try turning it off for awhile?

Any question is a good one right now. I appreciate any help at all since no one has to take time out of their day to help a stranger.

No he is not in 4 low. And he stopped to sleep for the night and today it is doing the same thing. I also had him disconnect the battery for 10 minutes just in case it may reset. Also, DIRTYMAX2004, based on what you've said, it doesn't sound like the truck is in limp mode at all.

I did get a bit of new information though which is that... not only is the speedometer reading twice as fast as it's supposed to, but the odometer is turning twice as fast as well. Nothing new to report other than that though.

This sure is a head-scratcher. I'm getting the feeling that it has something to do with the electrical system.

any updates or progress?

Well he made it home safe, late last night. I'll be taking it down to the shop tomorrow.

let us know what the issue was please....glad to hear he made it home

i own a dodge so i don't know how different our situations may be, but i had basically the same thing happen to me before. i pulled onto the interstate and the truck would not get over 45. no lack of power or anything, just would not shift into fourth. it all wound down to a bad ground on one of the batteries sending a messed up electrical charge to the computer. the speedometer really confuses me though.
good luck with it n let us know what ya figure out

40 MPH
 

Is this a 4X4? it sound like stuck in 4WD!!
wrench

Well I wasn't able to pick up the truck until Friday evening, and of course the shop isn't open on the weekends, so the truck will be sitting here until Monday.

I did talk to the guy at the repair shop and he told me to check the VSS (Vehicle Speed Sensor) for debris or loose / cut wiring. I know it's toward the rear of the truck, but I don't know what I'm looking for. Does anyone know where I could find this on my 2004 Chevy c4500?

I'd like to at least check it before I take it in the shop tomorrow morning. Thanks.

PS. The battery wiring seems to be squared away, and no it is not a 4x4.

Im curious what is wrong. Please post up what they find out.

yes filter can get plugged with 5 miles. is it 4 wheel drive maybe he hit 4low by accident if nothing else is wrong

i think that he said at least 2 times that it is NOT 4x4

Well the truck is in the shop. The mechanic called me and said he changed out the VSS (Vehicle Speed Sensor) and it still isn't working right. He can't find anything else wrong and there are no codes at all.

He says that he thinks the ECM is a bit haywire and reading the wrong speed and recommends getting the ECM reflashed. They can't do it there, and the local dealership can't work on these trucks, so my only option right now is to drive 170 miles (at 40 mph) to the nearest dealership that can reflash the ECM.

And he said that he isn't 100% sure it will fix the problem, but it's the only other thing he can think of. I'm having him change the fuel filter while it is there as a longshot, but it looks like I'll be heading out on a short, slow trip. Of course, if the reflash doesn't fix it, it's going to be a long trip home too. :s:

I'll post back with another update once I know more. Maybe it will help someone out in the future. Oh and thanks for all the replies and help guys. :tu: