deathwish

Hi all. Got an 88 D150 that is showing an error code 15 (VSS). I ordered a replacement Speed Sensor which arrived today. I'm planning on replacing it this weekend, but wanted to see if anyone had any advice on the procedure. I haven't been under the truck yet to locate the sensor, so I'm hoping it's easy to find and swap out. Other than the sensor or a broken wire, is there anything else that might pop a 15 error code? I noticed the other day when driving the truck home that after driving at highway speeds for awhile, the truck would die when I came to a stop. Would start right up again but die at the next stop. I am hoping that the VSS fixes this issue as otherwise it seemed to run fine. Any advice or tips would be appreciated. Thanks.

RacerHog

What Scan Tool Did you use? You should have been able to look to see if the VSS was working or not?
Anyway.... Couple bolts and plug it in and retest it and clear the code and you should be good to fly.

If the truck has overdrive or lockup converter... the problem might be in the trans.
If it Shutters or lugs the motor down when coming to a stop...Look into that... But I dont think that set a code 15

deathwish

Hey Bob,

Just used the flashing Check Engine light to find the error code. I have an OBD II tool, but not an OBD I. I don't believe the truck has overdrive, but I'm not sure about a lockup converter. I do know the original owner custom ordered the truck from Dodge with a lower gear ratio for towing a 5th wheel (as well as a sunroof?!). Do you know of any easy way to tell if it has the locking torque converter?

Dave

78D200

Only two way to tell (maybe three), pull the tranny and look at the input shaft, find the build sheet and see what it says or bring the VIN to a dealer and see what they can pull up for info.

78D200

I've heard about speed sensors messing with how the motor idles after coming to a stop. Install the speed sensor (either in the tranny or on the rear axle), take her for a spin and see if the shutter/dieing happens again.

EDIT: looks like the sensor is going to be in tail housing of the transmission.

78D200

Code 15 relates to a failure in the vehicle speed sensor circuit. The job of the vehicle speed sensor is to inform the computer about the speed of the vehicle so the computer can calculate engine load and prepare the engine idle speed control system while the vehicle is decelerating. On deceleration, the idle speed control system will allow additional air flow into the engine as the vehicle rolls to a stop. Usually code 15 will be accompanied by erratic speedometer readings (or no reading), erratic AT gear shifting, TCC lockup clutch instability, and intermittent or complete failure of the cruise control.
The VSS is a permanent magnet variable reluctance sensor that is mounted to the transmission or transfer case tail shaft. The sensor output is a series of pulses, the frequency of which are proportional to vehicle speed.
The most likely causes of VSS problems are:

• dirty or corroded contacts at the VSS
• bad sensor.
• stripped sensor drive gear
• dirty or corroded contacts at the PCM
• broken wire
• bad PCM

Remove the connector from the sensor and clean the contacts on the sensor and connector. Remove the sensor assembly from the transmission and check the drive gear. Reinstall the sensor (index it correctly) and reconnect the wiring. Disconnect the battery for 15 seconds to reset the fault, then drive for a while and see if the problem reappears. If it does not, you have fixed the problem.
To check the vehicle speed sensor, disconnect the electrical connector to the sensor. Using a voltmeter, check for reference voltage to the sensor. Connect the positive probe (+) to the orange wire terminal and the negative probe (-) to the black/light blue wire terminal. The reference voltage should be approximately 8.0 volts. Next, check the signal voltage from the PCM. Connect the positive probe (+) to the white/orange wire terminal and the negative probe (-) to the black/light blue wire terminal. The signal voltage should be approximately 5 volts. If there is no reference or signal voltage available, or the ground is missing, trace each back to the PCM and check the voltage there (8.0V is terminal 7, signal is pin 47, and ground is pin 4). Repair any wire or the connector if a voltage is present at the PCM but not at the connector. If the voltages are not present at the PCM, remove and reconnect the PCM connector and recheck - it is possible that the PCM connector has some corrosion on the terminals. If connector removal and replacement did not correct the problem, the PCM is probably bad - have the PCM diagnosed with a scan tool.
The best way to test the vehicle speed sensor circuit is with a scanner while driving the truck. If the scanner detects a signal from the vehicle speed sensor, it will display a reading other than zero and the speed signal should vary smoothly with the vehicle speed. If you have access to a scanner or oscilloscope, typical waveforms for good and bad sensors are shown below.

deathwish

Thanks for the info and the writeup 78D. I will hopefully know more this weekend once I get the unit replaced and I will post back as to whether that clears my code and also if it fixes the issue with it dying at a stop sign.

pro-tech

Fifth wheel on a D150 wow dont see that much.. They usually are 250 s or 350s I wouldnt pull a fifth wheel with that light of a truck. its just asking for trouble...Good luck with your fix its been well covered...Bill

deathwish

Well actually, I was told the original owner ordered this truck with a different rear end and intended to run a 5th wheel with it. I do not see any evidence that he actually did, but the truck does have two trailer connections built into the driver's side bed wall. He may have ordered the truck with a locking transfer case as well. The gentlemen I bought the truck from got it from the original owner, but that was several years ago. The truck sounds like it's turning a lot of rpms at highway speed. Wish I knew for sure exactly what I had.

deathwish

I found the VSS on the side of the tranny and found that the plug was not even connected to it. It was also quite loose and of course filthy. I pulled the old speed sensor out and replaced it with a new one. I also cleaned the plug with electronic cleaner and a straight pin to make sure it made a good connection to the new VSS. Pulled the negative battery cable for about 2 minutes, hooked it back up and checked the codes to make sure #15 was gone. It was. I then took the truck for a test drive.
I noticed that the truck had a major hesitation when pulling away from a stop unless you were very easy on the gas. This appears to be a new issue. Other than that, I drove it around till it warmed up and the truck never died on me. That's an improvement. Got home and pulled the codes and error code 15 had returned. Crap! I am assuming it's the connector or a wiring issue at this point. The only other code was 12, which is expected after disconnecting the battery. I will pull the connector and clean it again tomorrow and see how far back I can trace the wiring. Will had to track down that hesitation as well. Maybe I'll pull the plug on the TSS and see if that is causing my hesitation as I did not have that problem until today.

78D200

Is this truck TBI or Carb? If TBI I'm wondering if the computer lost it's parameters and needs to "relearn" them. I've seen this on 1st Gen Jeep GC vehicles and some of the pre-Magnum Dodge trucks. Not sure if its the same issue you are having though.

When you cleaned the connector, did you let it dry out completely before reconnecting it? Just wondering if some cleaner was left behind inside the connector causing a misreading.

deathwish

The truck is fuel injected so your theory about the ECM needing to relearn parameters after disconnecting the battery could be true. Haven't had time to do any work on the truck today, so nothing new to report.

I wiped off the connector, shook it and blew it out as best I could, but it's very possible there was some dampness from the electronics cleaner left. Time and weather permitting, I'll take the truck out tomorrow as is and see if the hesitation is still there. Then I'll clear the codes and drive it again and see if 15 pops back up.

RacerHog

Lets see if I can get this to work For you....

DR-3A Fault Code 15-Speed Sensor Circuit Complete Driveability Test 1-Step A, before proceeding.

1. Connect diagnostic readout box to engine harness connector, then start the engine.
2. Disconnect speed sensor connector, then enter the system into Engine Running Test Mode 71.
3. Connect a jumper wire between the T9 black and the G7 white/orange terminals of the speed sensor harness connector.
4. If display on readout box changes while making and breaking connection, replace the speed sensor.
5. If display on readout box does not change while making and breaking connection, proceed to Step B.

This is for your code 15 VSS test for you system...

If this is all working good...Then you just need to do the drive cycle because of the battery Disconnect.... This my require up to 40 key and temp cycles....
Warm the vehicle up before driving....

deathwish

Thanks RacerHog. BTW, do you have a recommendation for a Diagnostic tool? I have a good OBD II unit for my other vehicles but have just been reading the check engine flashes on the truck.

RacerHog

I think the DBR-2 will work back to 88...
IF not look into a OTC monitor 2000 or 4000.Snap-On MT-2500..Should one of them should help you get it done. What ever you can get your hands on to test it. (Barrow)

If you cant go that route then just try Ohm out the wires from the PMC to end of the sensor connector, Just to make sure the wire (s) are good...

deathwish

Excellent. Will look in to getting one of those!
Thanks again

lady blue

91 Chrysler Imperial with digital dash Speedometer not working. Disconnected electrical trans would not shift. Change sensor & connected wiring. Tested connector. Power is there. Changed Headlight switch. Still not working. Engine has no power. Limp mode? Engine acts like it is out of Gas but tank is full. I have replaced speedometer, Headlight, dimmer, ignition switch 2 times for each. Why? Electrical burning of wires & connectors & parts. The problem started 2 winters ago. Intermittent speedometer. Now? Nothing. all gauges in accurate. No Odometer. Had Computer rebuilt at Autozone & replaced Alternator due to inconsistent Voltage. Now my alternator is putting out 16 volts all the time. I drove today after all repairs & engine has no power & acts like it is running out of Gas when tank is full. I am at my end of investing any more money for a vehicle I only drive during winter. I found a problem as to why I have no power. Some nice mouse made a nest in the air intake which is also the ECM. The ECM is putting out 16.7 volts? I think the Mouse may have caused this to melt down? I went to a Recycling yard & found another Chrysler like mine? Wrong? I took the ECM speedometer & many more parts to fix up my Chrysler. Most fit but still am experiencing problems. No speed or Left front speaker. I have hot wired my Hazard Flashers to work. I found the Electric control module for ABS is disconnected? Reason for the constant trouble light. DO NOT TAKE YOUR MOPAR IN TO A PLACE THAT TELLS YOU THEY CAN RESOLVE TROUBLE LIGHT PROBLEMS. RIP OFF. I don't know how the Shade tree mechanics stay in Business?