Engine/Transmission (1998.5 - 2002) Speedometer acting up

[Kent Kuykendall]

Does anyone know what could cause my speedometer to stay at Zero till Truck gets to about 20-30 or so, then pop from zero up to current speed? When slowing down it does the opposite. Goes from about 30 or so and then right to zero. I figure it must have a bad sensor or something.



Can anyone shed some light?



Thanks in advance.



Kent

 

[Bob4x4]

Odds are very good it could be your rear wheel speed sensor



Bob

 

[Kent Kuykendall]

Could this also effect anti lock Brakes? Light has been on for a while.



thanks Kent

 

[blkdragon]

speedo

Yes, the speedo gear in your rear end is probley bad it will affect the ABS with the truck and when my gear was bad the brake light stayed on the light that comes on when your ebrake is on.

 

[GWilber]

Sounds like everyone agrees that the rear wheel speed sensor is your problem. My truck had a similar situation, but the speedometer didn't start working until 55 at first and then above 75 for a few days before quitting all together. After replacing the sensor everything works great. No more warning lights and the cruise even works.

I bought mine at www.magauto.com[url] (800)559-6698 _______________ 98. 5 QC 3500 5sp with 422,200 plus miles

 

[Kent Kuykendall]

Thank you all for the quick reply's. This site amazes me. I have never asked a ? that someone did not have the answer to. I will check on this part. How involved is it to change it out?



Thanks again



Kent

 

[ProspectorTim]

Thank you all for the quick reply's. This site amazes me. I have never asked a ? that someone did not have the answer to. I will check on this part. How involved is it to change it out?

Thanks again

Kent

The forums "search" function works real good too!
It took me about 2 minutes to find my exact problem described here.

A little over a week ago my ABS and Brake lights came on and stayed on. I checked the fuse - it was ok. I figured if the sorry RWAL was malfunctioning, that is an IMPROVEMENT to my truck; ignore the lights, explain it to the wife.

Well, this week I noticed the speedometer was erratic at low speeds (25 & 35 MPH speed zones on a military base) - exact symptoms described in Kent's first post.

Now that I know what the problem is, I guess I ought to fix it.

 

[GregBarnes]

Speedometer not working, ABS and Brake Light on

Thanks to all members. Had my brake and ABS warning lights come on and the speedometer did not work below 30MPH. Yes indeed it was the rear wheel speed sensor. The part was $46. 00 and took about 20 minutes to replace. All good now! Thought Id add to this for others.

 

[BSmalley]

I think my speed sensor is gone bad too. Driving down the interstate the other day on cruise, when truck just took off under full throttle. Shut the cruise off and truck was running fine, but noticed that the speedo was jumping back and forth. Each time I have driven the truck since then, the speedo was acting up, bouncing from 0 up to about 70. Initial problem on the interstate happened just as I hit a bridge expansion joint ( pretty good bump). My question is, does anyone have the part number for the sensor?

Thanks

Bill

 

[Kyle]

Amazing! - Thanks to all

I've been having the same problem for 2-3 days now (no speed indicated until it jumps up to 30, brake & abs light on all the time, etc. ).



I did one search and found my answer in the 2nd thread I clicked. Counting this reply, I've spent about 90 seconds on the diagnosis.



This forum is amazing!



Many thanks to all!



Does anyone have any tips on replacing the rear wheel speed sensor? Is it in the pumpkin? Do I have to drain the fluid or does it just screw in the top? Does it need to be adjusted for distance from the magnet? etc. , etc.



Any help or tips would be most appreciated -- even though it seems like I got my money's worth already.

 

[rickhans]

Earlier this yr the wire broke on the rear speed sensor and the only thing that quit working was the abs and brake lt. came on. Speedometer was erratic. Odometer still worked as did cruise control.

Now all systems have failed involving speed. Speedometer and odometer are dead. Odometer frozen at last numbers. Cruise does not work, and abs lt. is on. Svc. mgr. at dealership said there is a sensor on transmission that controls the speedometer, odometer, & cruise and will act up if the rear sensor fails, but not totally quit.

Problem - parts says there is no such part listed for a 5 sp. 98. 5 diesel ram and knows of no other part that could have failed. I put in a new rear sensor and pig tail so it should not have failed, and if it did, should not cause this much failure. Anyone have an answer?

 

[Bob4x4]

Earlier this yr the wire broke on the rear speed sensor and the only thing that quit working was the abs and brake lt. came on. Speedometer was erratic. Odometer still worked as did cruise control.



Now all systems have failed involving speed. Speedometer and odometer are dead. Odometer frozen at last numbers. Cruise does not work, and abs lt. is on. Svc. mgr. at dealership said there is a sensor on transmission that controls the speedometer, odometer, & cruise and will act up if the rear sensor fails, but not totally quit.



Problem - parts says there is no such part listed for a 5 sp. 98. 5 diesel ram and knows of no other part that could have failed. I put in a new rear sensor and pig tail so it should not have failed, and if it did, should not cause this much failure. Anyone have an answer?

The sensor your svc manager is talking about is an output speed sensor... ... ... auto only!Not manual trans:-laf

Time to do some diag work not guessing



Bob

 

[rickhans]

I don't guess at anything. Part of the diagnostic work is to first find out how the speed info gets to the speedometer and odometer. Since total failure of the abs controller on the differential does not cause total failure of the speedometer system, there has to be something else sending the info to the computer. I have not been able to find a '98 electrical schematic to trace down the wiring to the origin of the signal to the computer.

Since the service manager was wrong, I probably will have to rely on someone on this forum to give me some technical info. Perhaps someone has the wiring schematic on a pdf and could email it to me.

Anyone else out there know?

I probably will try the 911 forum where more may see this. I am pretty much grounded until I can get this problem solved and need to tow out of town Monday.

 

[obert]

Rick,-- My service manual CD is currently MIA, so I cant proove it with print. I have a 98. 5 24V QC 4x4 LB 3:54 5sp. Been thrugh it litteraly inside and out. It has 2 speed sensors. One is on the engine reading the crankshaft, the other is on the rear diff and reads the ring gear. Just my experience on a very simialr truck.



It sounded like your service mgr was the one doing the guessing, and not very well I'd say... ...

 

[rickhans]

I have a discussion going on 911 but will end it shortly. The rear sensor wires had come off. Speedo & odo now work, cruise does not, and engine dropped to idle again with codes P0121, throttle position sensor, and P1693 which was undefined. I will search for this. I checked the brake switch that cuts out the cruise and it is working correctly. I will have to find a schematic to track down the cruise control circuit.



You are talking about the crankshaft position sensor. I don't know anything about how it functions but understand that it can cause the engine to completely quit and not start.



Thanks.