Alright...as some of you know (ranger pilot, pawpaw) I have been having problems with my truck. 98 Ford Ranger 4.0 V6. Was shifting hard between first and second...O/D light flashing, and air bag light flashing....changed the ABS speed sensor on the rear differential, reset the computer, and everything seemed fine..drove it about 20 minutes, and it was shifting smoother than ever before...thought all was well! then all of a sudden...O/D light starts flashing again, and shifting hard between 1st and second, and 2nd and 3rd...wasn't on the highway so I couldn't get up to highway speed....stopped...turned off the truck, turned it back on, and everything was fine again...WIERD!! Drove home, and here I am....any thoughts?!? So confused

 

Sounds like a sensor problem or a problem with the PCM itself (doubt it). Clearing the computer removed all the bad data that was causing your problem.

I've run into this on my truck when battling the EGR system - clear the codes and start driving thinking everything is fixed - then it comes back. Somewhere there is a sensor or mechanism that a sensor is compensating for.

 

yeah....I figure it has to be a freakin sensor somewhere..I just don't even know where to start...Should I take it to the Ford place, or will another reputable mechanic in town be able to run the right diagnostics to determine what it is?

 

Since you have a flashing OD light, you should have a code stored. You need to pull it (same as for a CEL).

The PCM is detecting a problem with the transmission and is dropping it into failsafe (limp) mode. This maxes out EPC pressures and cause extremely harsh shifting. Cycling the ignition usually resets the limp mode until the next time the PCM detects the fault.

Limit your driving when in limp mode. Failure to do so may result in internal damage due to the high hydraulic pressures involved.

Get the codes first! Without them, you might as well fart into a hurricane.

Steve

 

Still sounds like a bad speed sensor/circuit. Did you check the integrety of the harness and connector and clean things up real good?

 

Well if the symptoms are the same, I'd suspect something is still wrong with the ABS speed sensor or it's wiring.

Just because a part is new, doesn't automatically make it good.

"Murpheys Law" says so too & believe me, it's still alive & functional, don't ask how I know thisl!!!! lol

SO, what to do, to isolate this problem???

Well the fact things straightened up for a spell, tells us the root cause of your problem is likely in the speed sensor, or it's ABS circuit.

You could do a resistance check of the new speed sensor, to see if it's coil is within resistance limits. I don't have a resistance value for the Ranger, perhaps someone else can post that resistance number.

FWIW, my 94 Taurus speed sensor resistance value is 200 ohms, so I'd expect the Rangers is in that range. Certainly if it reads a very low, or high resistance value, something is wrong.

The other thing to do & maybe the best thing, is to come by a scan tool, that can montor PID's & thus the speed sensors live output, through the under dash diagnostic port, while the vehicle is in operation & it's acting up.

If the speed sensors output is corrupt & it likely is, it'll show up on the scan tool.

ALSO If it's acting up, your speedometer should be erratic, as it's also taking clues from the speed sensor to operate.

SO, make sure the speed sensor is properly mounted & fastened in place, with it's 10mm fastner & it's electrical connector is plugged in properly & it's pins, sockets & wires are clean & undamaged.

If all is well at the speed sensors connector, follow it's wiring foward & look for trouble spots, where there are more electrical connectors, or spots where wire chaffing is likely.

Also, if the speedometer ISN'T acting up check or try swapping the ABS system main power relay, in the under hood power distribution box, if you haven't already done so.
If this power relay is intemittent, it can cause havoc with the ABS system & we all know how many problems these pesky relays cause, with the fuel pumps & PCM's, so it deserves to be on the suspect list imo!!!!

If all that checks out, suspect the new speed sensor is bad. BTW, was it a Ford, or aftermarket part?????

Let us know what you find.

 

there is no code...tried pulling it yesterday...just says it passed with flying colors HAHA...so I know it has to be electrical/sensor. The harness that I plugged back into the new ABS sensor looked to be OK. And as I said...it was shifting smoother than ever before...and then all of a sudden...bang...back to shifting hard, and OD light flashing. turned off the truck...read the codes...passed...turned on the truck without resetting the computer, or disconnecting the batter, and bam...right back to smooth shifting and running fine.

On a side note...and this may be related...may not...a few weeks ago, the airbag light was flashing sporadically...now...it (airbag dash light) doesn't flash, but the off light by the passenger airbag keyhole is stuck on.

 

and paw paw...the speedometer is fine...it has never acted up...it does seem to be a few miles per hour off...but I assumed that is because the tires on there now are not the factory tires, and seem to be a bit larger than factory tires...I bought this truck used about 3 years ago.

 

Well if the speedo isn't acting out, or the cruise control isn't dropping out, maybe look to the ABS power relay, in the under hood power distribution box, maybe swap it for, say the AC relay & go for a drive & see how it does!!!!

 

never messed with relays before....so relays are relays? it won't matter which one I swap it out with? I mean of course pick a system that isn't critical, like the AC...but other than that....it would be ok to swap them to see? Thanks

 

Well it needs to be the same part number relay, so it's internal connections & switchable power rating is the same, but many systems in the distribution box use the same relay, so a swap with the same P/N relay, from another system, not needed to operate the engine, would work.

These relays are common problem points for other systems, like the fuel pump & computer, so I think it has earned the right to be on your suspect short list, at this point.

Maybe it's ok, but lets test and see what happens, maybe you'll get lucky.

If it's bad, you can get them for between $5 & $10 at most autoparts stores, or the Ford Dealers parts counter.

The failure rate is so common, many folks now carry a spare or two in the glove box, sorta like fuses, just in case!!!! lol

 

paw paw...another quick question for you....is it possible the air bag light, and this is related? I read a few other posts about connections under the seat that could be loose? How hard are these connectors to get to? Is their any connectors under their that could cause the truck to shift hard and O/D light flash?

 

Ok this is why I started my thread about diagnostics, you have several codes from different systems that keep coming back after clearing and replacing sensors. The absolute first thing that should have been checked and need checked is the grounds for the PCM. If you have to get a wiring diagram then do it, but when multiple codes show up and keep coming back then 8 times out of 10 it has to do with the ground system.

 

Are you talking about codes from the OBD that are read on readers like they have at autozone? Are they stored? Because if so, there was no code when it was checked. The diagnostic tool said it passed. And that was after it was acting up. So wouldn't the code be stored?

 

No, that code reader will read engine codes, but not neccesarily drivetrain codes, ABS codes, or airbag codes (it's pretty basic code reader that only reads the minimum) What i am talking about is that you had both the OD light on and the airbag light on, thats multiple codes, they are probably stored but may be irrelevant in this case expecially since you already replaced the sensor and it didn't fix the problem. the airbag does use the speed sensor (passive restraint system is disabled until it reaches a preset speed usually 25mph, which is why you won't get an airbag deployment in a parking lot collision) You need to really check out all the ground wires for all the systems, I have seen cars still under the 3/36 warrenty with corroded off ground cables and start throughing codes, that no amount of sensor replacement will fix, and like I said 8 times out of 10 it takes a $6 ground strap to fix the entire problem.