Code 15 - No Keep Alive Memory power to PCM pin 1 or bad PCM (Memory Test
Failure). The voltage to the Keep Alive Memory (KAM) is missing (wiring problem)
or the KAM is bad. The KAM holds all of the settings that the computer "learns" as
it operates and all the stored error codes that are generated as a result of
something malfunctioning while the engine is running. Use a voltmeter to check
the voltage to the pin 1 on the computer - you should always have 12 volts. No
constant 12 volts = bad wiring. If you do always have the 12 volts, then the KAM is
bad and the computer is faulty.
If the computer has to "relearn" all the optimum settings every time it powers up,
the initial 5-30 minutes of operation may exhibit surges, poor low speed performance,
and rough idle.
Note that some aftermarket chips will cause code 15 to set. Remove the chip,
clear the codes and retest.
Before replacing the computer, remove the battery ground cable for about 20
minutes. This will clear all the codes. Retest after several days of running. If the 15
code is gone, then don't worry about it. If it is still there, then you get to do some
troubleshooting.
Wiring diagrams for the proper model years are next…
For 86 models see
http://www.autozone.com/images/cds/gif/large/0900823d80167158.gif
For 87 models see
http://www.autozone.com/images/cds/gif/large/0900823d8016715e.gif
For 88 models see
http://www.autozone.com/images/cds/gif/large/0900823d80167162.gif
For 89-90 models see
http://www.autozone.com/images/cds/gif/large/0900823d8019595f.gif
For 91-93 models see
http://www.autozone.com/images/cds/gif/large/0900823d80195960.gif
See the following website for some help from Tmoss (diagram designer) & Stang&2
Birds (website host) for help on 88-95 wiring
http://www.veryuseful.com/mustang/tech/engine/
Diagram courtesy of Tmoss & Stang&2birds
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif
Code 67 - clutch not depressed (5 speed) or car not in neutral or park (auto)
or A/C in On position when codes where dumped. Possible neutral safety switch or
wiring problem. This code may prevent you from running the Key On Engine On tests.
You can generally ignore this code, since it has no effect on engine performance.
The computer wants to make sure the A/C is off due to the added load on the engine
for the engine running tests. It also checks to see that the transmission is in
Neutral and the clutch depressed (T5, T56, Tremec 3550 & TKO)). This prevents the car
from being driven while the computer is in test mode. Key On Engine Running test mode
takes the throttle control away from the driver for several tests. This could prove hazardous
if the computer was jumpered into test mode and then driven.
The NSS code 67 can be bypassed for testing. You will need to temporarily ground
computer pin 30 to the chassis.
Code 81 – Secondary Air Injection Diverter Solenoid failure AM2. The solenoid valve
located on the back side of the passenger side wheel well is not functional. Possible
bad wiring, bad connections, missing or defective solenoid valve. Check the solenoid valve
for +12 volts at the Red wire and look for the Lt Green/Black wire to switch from +12 volts
to 1 volt or less. The computer controls the valve by providing a ground path on the
LT Green/Black wire for the solenoid valve.
With the with the ignition on, look for 12 volts on the red wire on the solenoid connector. No
12 volts and you have wiring problems.
With the engine running, stick a safety pin in the LT Green/Black wire for the solenoid valve
& ground it. That should turn the solenoid on and cause air to flow out the port that
goes to the pipe connected to the cats. If it doesn't, the valve is bad. If it does cause
the airflow to switch, the computer or wiring going to the computer is not signaling the solenoid valve to open.
Putting the computer into self test mode will cause the solenoid valve to toggle.
If you listen carefully, you may hear it change states.
Code 95 Key O, Engine not Running - the following test path is for 86-90 model Mustangs.
The 95 code is because at one time or another, the fuel pump relay hiccupped and
didn't provide power the pump when the computer told it to run. Sometimes this
is a one time thing, other times it is a no run or runs poorly condition.
To help troubleshoot the 95 code, follow this link for a wiring diagram
http://www.autozone.com/images/cds/gif/large/0900823d80167162.gif
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 driver’s 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. 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. If there is good voltage there & at the Pink/black wire, swap the relay.
Some Mass Air conversions neglect to run the extra fuel pump wire, and they always have a 95 code.
See
http://www.stangnet.com/tech/maf/massairconversion.html for more information on the Mass Air wiring conversion.
There are no valid code 30 or 40 for a 5.0 Mustang. Are you sure that it isn't a 34?
Your O2 sensor volage reading are low. You O2 sensors may be on the old side, you have
a vacuum leak, or other lean mixture problem.
Are you sure that the MAF calibraion matches the injectors?