CODE 96: I need a good Electrical Troubleshooter!!! PLEASE!


Apr 1, 2011
Okay, I have had this problem for a year now.

It originally started when I had a code scanner in the TEST Mode and disconnected the two (2) ten (10) pin salt & pepper shaker connections to clean them. I know, big mistake. Anyway, I cleaned the connectors and plugged them back together. I noticed that then, my fuel pump started running and I could not shut it off. Everything was fine before this! I then disconnected the battery ... then reconnected and it again started running. I then replaced the fuel pump relay and it went back to normal operation. However, upon scanning it later after driving, I noticed a Code 96 kept coming up in the "Continous Memory" second set of codes during all KOEO tests. This has occured for a year now.

Anyway, the problem comes in in getting rid of this code. So far, I have changed the Fuel Pump relay, the EEC Relay, check my grounds (all less than 1 ohm) at 60 pin connector. Checked the Fuel Pump Monitor wire where it ties in to the main fuel pump wire behind drivers seat .... good soldered factory connection and it ohmed out fine and always has 12 volts. I drove around with a test light hooked up to this wire and the test light is always lit. The problem appears to be in the code definitions! this causes a wild goose chase which is trying my patience and wearing me out!!! Some code definitions say a Code 96 is "battery power "open" to PCM. And other information says its the fuel pump secondary circuit! And from my research, the "fuel pump secondary circuit is the battery wire to the fuel pump relay that then goes to the fuel pump when the relay is energized. So, which one is the right code??? I have also checked the primary fuel circuit which includes the PCM to inertia switch, to relay, back to the computer ground. But, between the three of these circuits, it is very time-consuming since I am all over the car!!! Which circuit is it REALLY in??? And, like I said above, it is an intermittent condition. The car is being driven daily and nothing is noticed while driving as far as the fuel system shutting off or anything like that. Some would say forget about it, but I cannot do that ... I need to find it and fix the problem since it probably affects other things. Purrs on the highway engine couldn't be smoother ... but at idle, it is somewhat rough. The vacuum is a bit low at 15 in Hg. but that is probably a separate problem that I haven't been able to figure out. Though I am very good at these systems, this car is giving me a run for my money and time!!! Anyway, if one of these circuits is open like the code says, then how come it runs great out on the road. Seems to me, if this is the case, it is getting power from an alternate route or it would be missing or cutting out! Anyway, if anyone knows how it could be getting power some other way I'd like some good input. I have painstakenly checked these circuits over and over for a year now. Just went through it again tonight. Drove the car for 12 miles and no Code 96 has showed up sop far. But, in a day, it will show up if not before I get back home. It is very intermittent meanly it is only happening over a long interval of engine running, but on a regular basis .... just about every day of driving, it will reset itself with the "Continous Memory" which causes me to again scratch my head ... please help me to solve this plagueing intermittent problem so I can move on to bigger and better things! BTW, I already have all of the schematics etc. and have traced everything .... just am not finding anything since it is so very sporatic ... but regular over the driving cycle.

Also, the fuel pump is about 2 years old. I do not want to drop the tank and spend two days just to find everything okay on such an intermittent condition ... cuz it probably would not be there at that moment. And the computer seems alright since everything else works and is acting the way it should. Something is setting this Code 96 Fuel Monitor Code ... does anyone know what else could be doing this or give advice on what else to check. I think I checked everything but certainly something could be hidden in a harness (not going to rip them apart w/o a problem indicator).

Any help or good technical suggestions would be appreciated!!!
  • Sponsors (?)

You forgot to post the year model of the car. There are 2 different wiring schemes and without knowing the year, I cannot post the correct test path for your car.
Its a 1990 Mustang GT with an AOD and original 5.0 engine.

I did find one of those test procedures a while back on the internet and read it for ideas but it was not exactly for my car. It could have been for a 4 cylinder Mustang or something like that. If you have the exact test procedure for my year etc. that might help a great deal!!! I've spent so much time on this already, following a script might be a lot easier! ;-) As always Thank You!!!
Code 96 – KOEO- Fuel pump monitor circuit shows no power - Fuel pump relay or battery power feed was open - Power / Fuel Pump Circuits. The fuel pump lost power at some time while the ignition switch was in the run position. The main power feed to the pump is what is losing power.

Look for a failing fuel pump relay, bad connections or broken wiring. The fuel pump relay is located under the passenger seat. On Mass Air Conversions, the signal lead that tells the computer that the fuel pump has power may not have been wired correctly. See Mustang Mass Air Conversion «


Look for power at the fuel pump - the fuel pump has a connector at the rear of the car with a pink/black wire and a black wire that goes to the fuel pump. The pink/black wire should be hot when the test connector is jumpered to the test position. . To trick the fuel pump into running, find the ECC test connector and jump the connector in the lower RH corner to ground.

86-90 Models:
Using the diagram, check the red/black wire from the fuel pump relay: you should see 12 volts or so. If not, check the inertia switch: on a hatch it is on the drivers side by the taillight. Look for a black rubber plug that pops out: if you don't find it, then loosen up the plastic trim. Check for voltage on both sides of the switch. If there is voltage on both sides, then check the Pink/black wire on the fuel pump relay: it is the power feed to the fuel pump. Good voltage there, then the fuel pump body to tank wiring harness connector is the likely culprit since it is getting power. No voltage there, check the Orange/Lt blue wire, it is the power feed to the fuel pump relay & has a fuse link in it. Good voltage there & at the Pink/black wire, swap the relay.

Keep in mind that the relay wiring and socket can also cause intermittent problems. Clean the relay socket with non-flammable brake parts cleaner or electrical contact cleaner. If you find damaged wiring at the relay socket, replacement pigtail socket assemblies are available at the auto parts stores. Be sure to solder the wires and cover the solder joints with heat shrink tubing if you replace the relay socket.

Hey Jrichker,

Well, I read this before and all checks out because I have checked it multiple times and the car is being driven. Checked for power and ohm-ed out the wires. The only thing I have not done is clean the connectors per se or the ones I can get to w/o tearing the car apart. I can try that shortly. As I read through I have everything everywhere as mentioned but it is intermittent that the code is being set and is unnoticeable to the driver apparently! Any ideas?

Also, the connector shown at the bottom of your page, what connector is this, the one at the fuel tank? I hate to pull the fuel tank and spend to days and nothing is fixed per se. Just too much work for a wild goose chase. Seems like this Code 96 has to be something more since it only started when the relay went bad due to re-connecting on eof the 10 pin connectors with the code scanner energized. Before that, never say the code whatsoever ... so that tells me it is not just a dirty connector or something like that. Any ideas?

Also, At the beginning of your response, it states it is the power circuit to the fuel pump which powers the fuel pump. This is what I have been checking proimarily since this is what they seem to be terming the secondary fuel pump circuit. Just am NOT finding anything .... it works and checks out! But, why do other code listing say power to ECM open @ some point? that is a entirely different circuit? Or could we all have it wrong and it also involves the primary circuit which involves the Inertia Switch and a bump is momentarily setting this code off? Just guessing here ... this seems more likely than what I am finding cuz I am not finding anything! But, again, everything has been checked and is working. Its only apparently doing it for a millisecond and sometimes not even after driving 12 miles. That is intermittent. Any ideas cuz everything has been checked???

I shall clean the Fuel Pump relay connector and maybe pull the wires and look for any damage here since the relay here went bad .... just do not know what else to check within reason w/o unwrapping every harness on the car or removing the gas tank. Any other ideas???

Could you answer each one of these questions with some feedback ... as always THANK YOU!!!
The connector in the drawing is the one inline with the body connector. Usually it is under the car, on the passenger side just aft of the spare tire well.

Notice in the wiring diagram that a pink/black wire runs from the fuel pump relay to pin #19 on the computer. That wire is the fuel pump power sense wire, and if it has a loose or bad conncetion, it will set the code 96. There is one harness connector that joins the fuel pump relay harness to the main computer wiring harness. It is located up near the computer and is under the passenger side kick panel. The connector has several other wires that feed power to the relay coil and control the relay to make it turn the fuel pump on and off.

I am including the complete fuel pump test path to show how the circuit works.
Fuel Pump Troubleshooting for 86-90 Mustangs

Revised 30-Aug-2008 to update fuel pump wiring diagram

Clue – listen for the fuel pump to prime when you first turn the ignition switch on.
It should run for 5-20 seconds and shut off. To trick the fuel pump into running,
find the ECC test connector and jump the connector in the upper RH corner to



If the fuse links are OK, you will have power to the pump. Check fuel pressure –
remove the cap from the Schrader valve behind the alternator and depress the
core. Fuel should squirt out, catch it in a rag. A tire pressure gauge can also be
used if you have one - look for 37-40 PSI. Beware of fire hazard when you do this.

No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – press reset button on the inertia switch. The hatch
cars hide it under the plastic trim covering the driver's side taillight. Use the
voltmeter or test light to make sure you have power to both sides of the switch

B.) Fuel pump power relay – located under the driver’s seat in most Mustangs built
before 92.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) Blown fuse link in wiring harness.
F.) Fuel pressure regulator failed. Remove vacuum line from regulator and inspect
for fuel escaping while pump is running.

The electrical circuit for the fuel pump has two paths, a control path and a power

The control path consists of the inertia switch, the computer, and the fuel pump
relay coil. It turns the fuel pump relay on or off under computer control. The
switched power (red wire) from the ECC relay goes to the inertia switch
(red/black wire) then from the inertia switch to the relay coil and then from the
relay coil to the computer (tan/ Lt green wire). The computer provides the ground
path to complete the circuit. This ground causes the relay coil to energize and
close the contacts for the power path. Keep in mind that you can have voltage
to all the right places, but the computer must provide a ground. If there is no
ground, the relay will not close the power contacts.

The power path picks up from a fuse link near the starter relay. Fuse links are like
fuses, except they are pieces of wire and are made right into the wiring harness.
The feed wire from the fuse link (orange/ light blue wire) goes to the fuel pump
relay contacts. When the contacts close because the relay energizes, the power
flows through the contacts to the fuel pump (light pink/black wire). Notice that
pin 19 on the computer is the monitor to make sure the pump has power.
The fuel pump has a black wire that supplies the ground to complete the circuit.

Remember that the computer does not source any power to actuators, relays
or injectors, but provides the ground necessary to complete the circuit. That
means one side of the circuit will always be hot, and the other side will go to
ground or below 1 volt as the computer switches on that circuit.


Now that you have the theory of how it works, it’s time to go digging.

Look for 12 volts at the Orange/Lt. Blue wire (power source for fuel pump relay).
No voltage or low voltage, bad fuse link, bad wiring, bad ignition switch or ignition
switch wiring or connections. There is a mystery connector somewhere under the
driver’s side kick panel, between the fuel pump relay and the fuse link.

Turn on the key and jumper the fuel pump test connector to ground as previously
described. Look for 12 volts at the Light Pink/Black wire (relay controlled power
for the fuel pump). No voltage there means that the relay has failed, or there is a
broken wire in the relay control circuit.

Check the Red/black wire, it should have 12 volts. No 12 volts there, either the
inertia switch is open or has no power to it. Check both sides of the inertia
switch: there should be power on the Red wire and Red/Black wire. Power on the
Red wire and not on the Red/Black wire means the inertia switch is open.

Pump wiring: Anytime the ignition switch is in the Run position and the test
point is jumpered to ground, there should be at least 12 volts present on the
black/pink wire. With power off, check the pump ground: you should see less
than 1 ohm between the black wire and chassis ground.


The yellow wire is the fuel tank sender to the fuel quantity gage. The two black wires are grounds.
One ground is for the fuel tank sender and the other is the fuel pump. The ground for the fuel pump
may be larger gauge wire that the fuel tank sender ground wire.

Make sure that the power is off the circuit before making any resistance checks. If the circuit
is powered up, your resistance measurements will be inaccurate.

You should see less than 1 Ohm between the black wire(s) and ground. To get some idea of what
a good reading is, short the two meter leads together and observe the reading. It should only be
slightly higher when you measure the black wire to ground resistance.

The Tan/Lt Green wire provides a ground path for the relay power. With the test
connector jumpered to ground, there should be less than .75 volts. Use a test
lamp with one side connected to battery power and the other side to the
Tan/Lt Green wire. The test light should glow brightly. No glow and you have a
broken wire or bad connection between the test connector and the relay. To test
the wiring from the computer, remove the passenger side kick panel and
disconnect the computer connector. It has a 10 MM bolt that holds it in place.
With the test lamp connected to power, jumper pin 22 to ground and the test
lamp should glow. No glow and the wiring between the computer and the fuel
pump relay is bad.

Computer: If you got this far and everything else checked out good, the computer is suspect.
Remove the test jumper from the ECC test connector located under the hood.
Probe computer pin 22 with a safety pin and ground it to chassis. Make sure the computer
and everything else is connected. Turn the ignition switch to the Run position and observe
the fuel pressure. The pump should run at full pressure.
If it doesn't, the wiring between pin 22 on the computer and the fuel pump relay is bad.
If it does run at full pressure, the computer may have failed.

Keep in mind that the computer only runs the fuel pump for about 2-3 seconds when you turn
the key to the Run position. This can sometimes fool you into thinking the computer has died.
Connect one lead of the test light to power and the other lead to computer pin 22 with a safety pin.
With the ignition switch Off, jumper the computer into self test mode like you are going to dump
the codes. Turn the ignition switch to the Run position. The light will flicker when the computer
does the self test routine. A flickering light is a good computer. No flickering light is a bad computer.
Remove the test jumper from the ECC test connector located under the hood.

Fuel pump runs continuously: The fuel pump relay contacts are stuck together or the Tan/Lt Green wire
has shorted to ground. Remove the fuel pump relay from its socket. Then disconnect the computer and use
an ohmmeter to check out the resistance between the Tan/Lt Green wire and ground. You should see
more than 10 K Ohms (10,000 ohms) or an infinite open circuit. Be sure that the test connector isn’t
jumpered to ground.
If the wiring checks out good, then the computer is the likely culprit.

Prior to replacing the computer, check the computer power ground. The computer has its own
dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to
it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a
black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire. You'll find it up
next to the starter solenoid where the wire goes into the wiring harness

If all of the checks have worked OK to this point, then the computer is bad. The
computers are very reliable and not prone to failure unless there has been
significant electrical trauma to the car. Things like lightning strikes and putting
the battery in backwards or connecting jumper cables backwards are about the
only thing that kills the computer.

See the following website for some help from Tmoss (diagram designer) &
Stang&2Birds (website host)


  • Underhoodpictures007-01.jpg
    60.1 KB · Views: 114
  • Underhoodpictures010.jpg
    103.7 KB · Views: 109