No start-Dodge Ram 96 B2500

Tiny
BOB B
  • MEMBER
  • 1996 DODGE RAM
  • V8
  • 2WD
  • AUTOMATIC
  • 125 MILES
96 Dodge ram B2500, 5.2 120k original miles.
Q: 3 days ago, after running well, Idle dropped, van stalled. Drove it home and next day checked codes.
505:Idle air control-short or open.
123:TPS sensor-voltage high
118:ECT voltage high
113:Intake air sensor:voltage high
1492:amb batt. Temp-too high.
Upstream 02 code was also there, so I replaced that. After replacement, no start, only cranking. Also replaced idle air control and TPS sensors, same condition. Found upstream 02 wires on female plug were all exposed. I isolated and insulated them today, no change. What next? No spark, no fuel it seems.
Do you
have the same problem?
Yes
No
Wednesday, February 9th, 2011 AT 4:47 PM

9 Replies

Tiny
BOB B
  • MEMBER
Also, all fuses are OK. Not sure about relays though.
Was this
answer
helpful?
Yes
No
Wednesday, February 9th, 2011 AT 5:16 PM
Tiny
CARADIODOC
  • EXPERT
All of those sensors didn't fail at once. All of the codes for voltage high suggests a break in the ground wire that is common to all of them. There are also four ground wires for the Engine Computer. Two of them are "signal grounds" meaning for the sensors. The other two are "power grounds" meaning they're for high-current items like injectors and the ignition coil.

Use a scanner to read live data. If all of those sensors still read high, measure the voltage on the three TPS wires. You should find 5.0 volts, 0.2 volts, and the middle signal wire will have somewhere near 0.5 volts at idle up to around 4.5 volts at wide-open throttle. If you find 5.0 volts on all three, there is an open ground wire someplace.

Caradiodoc
Was this
answer
helpful?
Yes
No
Wednesday, February 9th, 2011 AT 8:37 PM
Tiny
BOB B
  • MEMBER
Thank you! Just checked, but since it will not run, I can only check with ignition switch in "ON" position. I get 5 volts on all three TPS leads. Current codes show:123-high, 118:high, 113:high, 1492:high.
Was this
answer
helpful?
Yes
No
Wednesday, February 9th, 2011 AT 9:37 PM
Tiny
CARADIODOC
  • EXPERT
Perfect. That means the ground wire is open for all of those sensors. The crankshaft position sensor is on the same ground circuit. That's why the engine won't start. I only have a '99 service manual but I think it is the same. Follow the TPS wires about a foot to the larger harness that runs along the inside of the left valve cover. Follow that harness toward the back of the engine to just in front of the breather cap. There's a splice about an inch in front of where the rear injector wires go into that harness. Check there for a corroded splice. Another splice appears to be buried right over the front of that valve cover. The harness along the valve cover crosses a larger harness that goes across the front of the engine. The front injector wires appear to go into the harness right by that splice.

The last splice appears to be about a foot from the Engine Computer down that harness. The wire you're looking for is black / light blue. Before you tear the harnesses apart, see if you can back-probe the connectors at the Engine Computer. You might have to pop a protective cover off so you can stick a paper clip beside the wire to reach the terminal, but don't completely disassemble the connector body because they're nightmares to get back together. There's three rows of pins in the black connector. In one of the outer rows of pins, the black / light blue wire is the fourth one from the end. Measure the voltage there first, if possible. I think you're going to find 0 volts, but if you do find 5 volts, there's no need to look at those splices. If there is 0 volts there, that 5 volts from the sensors isn't getting back to that pin. That means there's a break in that wire between the Engine Computer and all of those sensors. The splices are the most likely places to find the problem but the wire could be cut anywhere.

Caradiodoc
Was this
answer
helpful?
Yes
No
Wednesday, February 9th, 2011 AT 10:53 PM
Tiny
BOB B
  • MEMBER
Thanks Cardiodoc, darkoiasc and raining now, so I will investigate more tomorrow morning. The no start situation began after the 02 sensor was changed, that is what drew my attention to the frayed harness(probably the root of the cause). I did surgically re-shielded all the wires and corrected that. Difficult for me, not being a wiring genius. I am assuming the black/light blue wire is on one of the three plugs connected to the ECM. I can't see with the insulation on. Would that be the 3rd plug, closest to the drivers side? I will look again in daylight. I appreciate your input on this problem, and should I get it going, will happily make a donation for your valuable time provided. I have no reliable technicians here I can rely on, so I will keep you updated until I find the answer. Thanks again, and have a great night my friend! Bob
Was this
answer
helpful?
Yes
No
Thursday, February 10th, 2011 AT 1:53 AM
Tiny
CARADIODOC
  • EXPERT
Thanks bunches. According to the service manual, the three computer plugs are all different colors. You want the black one.

Caradiodoc
Was this
answer
helpful?
Yes
No
Thursday, February 10th, 2011 AT 2:03 AM
Tiny
BOB B
  • MEMBER
Mine are all black, but passenger side and center have gray trim on PCM mounts. Driver side is all black. My Haynes schematics for 92 and later show all sensor grounds as light blue. I will look for your instruction first, and see if it matches what I have. I will begin with the all black plug and see where that takes me. Thank you:)
My manual is Haynes 30065 for Dodge Vans 71 to 2003.
Was this
answer
helpful?
Yes
No
Thursday, February 10th, 2011 AT 3:06 AM
Tiny
BOB B
  • MEMBER
Hi! After considerable testing and inspecting the wiring, it was the ECU that was malfunctioning because of the short in the 02 sensor wiring, which I repaired first. I replaced the ECU today and all is running well. This caused all the 5 volt sensor readings I was getting until I traced it all to the ECU. All other harness wiring was fine. Thanks for putting me on the right track to figuring it all out! Bob
Was this
answer
helpful?
Yes
No
Wednesday, February 16th, 2011 AT 3:37 AM
Tiny
CARADIODOC
  • EXPERT
If you're interested in performing an autopsy, you might want to take the computer apart to see if the copper trace for that ground circuit is burned open. That happened to a "bugged" car that I put problems in for my students to troubleshoot. There was a 1/4" long circuit between two pins that fed the alternator field on a '97 Dakota. While testing the system, someone grounded the wrong point and burned that circuit open. Later I added wires to it and a switch so I could switch the defect in and out as desired. I also took a few computers apart that had that gel material surrounding the circuit board. It doesn't take too much effort to peel those boards out, then you can rub the gel off to look at the backside of the pins.

Caradiodoc
Was this
answer
helpful?
Yes
No
Wednesday, February 16th, 2011 AT 4:22 AM

Please login or register to post a reply.

Recommended Guides