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Ask Dodgerench Your Own Question
Dodgerench, ASE Certified Technician
Category: Dodge
Satisfied Customers: 3404
Experience:  30+ years Dodge/Chrysler exp., ASE Master with L1 certification. Driveability/ combustion specialist
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96 dodge: pump relay..when unit key turned on fuel pump works..ign

Customer Question

I have 96 dodge ram with 5.9 .fuel pump relay will not cut on when unit key turned on fuel pump works if relay is man. tripped changed ign. switch and crank postion sensor checked all grounds truck orignnal just cut off going down interstate at 65.any suggestions.

Submitted: 7 years ago.
Category: Dodge
Expert:  Dodgerench replied 7 years ago.
HiCustomer welcome to Just Answer!.

Does your CHECK ENGINE lamp do a bulb test, burning about 2 seconds at key-on, Andy?
Do you know if you have spark at the engine?
Better yet, is there spark at the spark plug ends?

Have you had the engine scanned for codes yet?

If not, try the "flash code" method, something left over from the early days of Chrysler fuel injection. This is how it works...

Roll the key from off to on three times, leaving the key ON.

Watch the CHECK ENGINE lamp as it does a longer than normal bulb check (close to 5 seconds) and then goes dark.

When the CE light comes back, it will be flashing, so be ready to keep count.

The pauses between flashes tell you what to do. Short pauses mean you should continue counting... this digit isn't done yet.

Longer pauses mean the digit is completed and you're moving on to the next one.

All trouble codes are composed of two digits, like 12 or 55, so you will always have an even number of digits once the flash code process is over.

Repeating the process 2-3 times is highly recommended if you're not a flash code veteran... codes such as 12 often become... "3" if the pauses aren't recognized.

Talk shortly!
Customer: replied 7 years ago.
the truck is reading code 42 fuel relay
Expert:  Dodgerench replied 7 years ago.
That's the autoshutdown (ASD) relay that you found, a close cousin to the fuel pump circuit. The ASD supplies power to the coil and injectors, so loss of this input will certainly cause a problem like what you're seeing.

What I see in common with the ASD and fuel pump relays are the power feed to the control side of the relay.. the key-on feed that's used to power the electromagnetic coils that actually pull the contacts closed in the two relays to transfer power. There's a very good chance that you have neither spark nor fuel at this point.

Check the #9 fuse in the Junction Block, the inside fuse box at the left end of the dash. It's numbered and will be a 10-amp unit.

If blown, the engine may start with a new fuse, but the problem won't be solved. Fuses don't blow for no reason, so something overpowered it and caused your stall. Unfortunately, it gets a bit complicated...

This fuse supplies power to the control side of four relays... ASD, fuel pump, A/C compressor clutch and transmission. It's also powering your duty-cycle purge solenoid and EGR vacuum solenoid, any one of which (and wiring leading to it) could be the fuse failure problem.

Relays typically draw about 1/10th of an amp... virtually nothing on the control side. The purge and EGR solenoids will be the bigger power draws but are also pretty minimal. You may have to waste a few fuses in finding the problem, but these are the places to look.

The relays are all in the underhood fuse block (PDC), where the EGR solenoid is located to the right and rear of the throttle body (if equipped). Most markets don't use EGR in this year, but the wiring may still be present and can still short out.

The purge solenoid is located to the left and rear of the throttle body and WILL be present. It's the 2-wire unit with the two large vacuum hoses attached. I've never seen a shorting problem with the purge solenoid, but wiring in the area is always suspect due to the sharp upturned edges of the valve cover and protruding intake manifold bolt heads.

If the fuse holds and the truck runs, some wiggle testing on the engine harness will probably turn the short up. These things can be tough to find, so if it doesn't show up easily... take a few extra fuses with you the next time you go for a ride!

If you have any questions, problems (or the #9 fuse isn't popped), please write back and I'll be glad to help.

Customer: replied 7 years ago.
The #9 fuse isn't popped you can man engage relay and the truck will run getting spark at plugs
Expert:  Dodgerench replied 7 years ago.
OK.. Maybe I should've just asked you to check for two voltage sources under the ASD and Fuel Pump relays first lol! You may have a loss of power to those control feeds, so let's check that next. Remember... TWO power sources are what's required. If you find there to be problems in this department, check the transmission and A/C clutch relays as well. The purge solenoid and EGR (if equipped) are yet other places this feed is routed, so continue checking to see if ANY have power, which will help narrow the focus a bit. Ed
Customer: replied 7 years ago.

I have checked the power to these two places it does have it 12.7 volts to each

Could the ECM cause this problem in any way ?


Expert:  Dodgerench replied 7 years ago.
It's possible but sure not something I'd expect.
Which relay is it that you can manually override to get the engine running, Andy? The Fuel pump or ASD? Both?

Customer: replied 7 years ago.
The fuel pump you hear the ASD kick on when the key turns on but the fuel one will not do any thing
Expert:  Dodgerench replied 7 years ago.
Thanks. I'll look up the diagram for fuel pump control and get right back to you. We'll be checking from the fuel pump relay back to the PCM and an ohmmeter will come in handy.
Back shortly! Ed

Expert:  Dodgerench replied 7 years ago.
The fuel pump relay control circuit runs between the "C" connector of the PCM and the PDC fuse/ relay block via a brown/ white wire.

The C connector is the far-left of the three in your PCM and is colored black/ light grey I believe. It's installed in position C19 of the connector, something you can find easily by using the numbering cast into the open (terminal) end of the connector.
The opposite end arrives at the PDC at terminal 85 of the relay socket, something (once again) that can be found by looking at the underside of your relay for numbering.

You should have 5 ohms or less of circuit resistance between these two points.

If OK, reinstall the relay and turn the key on with the PCM C-connector still detached. Ground the C19 pin and listen to the relay or listen for fuel pump operation, as this should engage your fuel pump just as if the PCM was doing it.

If effective, check your relay for resistance between its 85 and 86 terminals, looking for a short that might have burned the PCM driver out that controls actuation of this circuit. Normal resistance of the ISO-20 relay used is right around 70 ohms. If you show substantially less resistance than that through your fuel pump relay control windings, this may have caused the driver to overheat and burn out since it would be carrying more current than designed.

Let me know what you find,

Dodgerench and 2 other Dodge Specialists are ready to help you
Expert:  Dodgerench replied 7 years ago.
And the PCM is located on the passenger side firewall underhood. Sorry!
Customer: replied 7 years ago.

The Pcm has a dead driver all the wies and relays checked out good.

Thanks for the help I would have pulled my hair out if I any. Thanks again

Expert:  Dodgerench replied 7 years ago.
That's something I don't see every day! I'd toss that relay just in case, Andy. Even if it checks OK for resistance, it might have an internal shorting problem that could take the new PCM out as well.

Hey, you COULD wire your ASD control circuit to the fuel pump's. It was done like that for years and years and I'm sure the driver could handle two tiny little relay control loads. If you'd like to try that instead of tossing the PCM, I'll be happy to send the wiring locations for the redirection. It would only involve cutting one wire and splicing it to the other.

Sound good?
Customer: replied 7 years ago.
Thanks I'll do that it might save a lot on a old work truck
Expert:  Dodgerench replied 7 years ago.
I can't see why it wouldn't work. We used a common driver for fuel pump and ASD forever before the JTEC controller like yours came along. Both relays are fired at the same time, so... OK I realize now why they don't do it that way any more.

It's OBD2 self-diagnosis. Oxygen sensor tests sometimes require the 02 sensors to be turned on overnight while the truck sits all turned off. They separated the fuel pump from the ASD so that the 02 sensors can be run without draining more power from the truck than necessary (02 heaters come from ASD).

Splicing those circuits together will get it running again but might produce battery or 02 sensor heater monitor issues down the road.

What do you think? Would you like to try it anyway? You'll need a good battery!