| Checking your Ford Mustang computer codes |
TYPES OF CODES
NOTE: Some people have problems
distinguishing the different codes. READ THIS SECTION CAREFULLY.
There are drawings of the code formats at the end of this section.
FAST CODES
Fast codes contain the fault information
output in the normal slow codes but are output about 100 times faster.
These are the first things output on a Key On Engine Off test.
HARD FAULTS
Hard faults are problems that the computer
has located RIGHT NOW. Examples are a sensor out of range or a broken wire (open circuit).
Hard faults are the FIRST set of slow codes output in a Key On Engine Off test. BEFORE the
SEPARATOR pulse.
In a Key On Engine Running test, there are ONLY HARD FAULT codes. These are output right
after the fast codes.
SEPARATOR PULSE
The separator pulse is a single pulse that
indicates the END of hard fault codes and the BEGINNING of memory codes.
It will show up as a code 10 on most digital testers.
MEMORY CODES
Memory codes are problems that the computer
has noticed in the past. If for example there was a loose wire to a solenoid that only
lost contact while driving but was making contact while testing the system there would be
NO HARD FAULT CODE. The code would show up IN MEMORY. The same would happen for a sensor
that only went out of range occasionally. Memory codes come out AFTER the separator pulse.
NOTE: The computer will erase the memory after a certain number of engine re-starts if the
problem does not repeat itself. The number of re-starts varies from 20 to 80 depending on
the year of the vehicle. The later models keep memory longer.
ENGINE ID
The engine ID in a running test is a series
of pulses equal to one half the number of engine cylinders. A 4 cylinder engine ID is 2
pulses, a 6 cylinder ID is 3 pulses and an 8 cylinder ID is 4 pulses. A diesel ID is 5.
GOOSE CODE
A "GOOSE" code (also called a
dynamic response test) is output during an engine running test. This is a single pulse to
signal you to quickly move the throttle approximately 1/2 way down and release. NOTE: Not
all engines give a "GOOSE" code.
CODE FORMATS
Codes are output as a series of pulses. The
following charts show the (approximate) timing of the various code pulses.
NOTE: Two digit codes are shown. Three digit codes have similar timing. It just takes a
little practice to distinguish between two and three digit types.
Click on the image to enlarge
TESTS
NOTE: Vehicle should be fully warmed for all
tests.
HOOKUP
See figure below. EEC IV vehicles have two
connectors for self testing the system. They are located on the firewall or the left or
right front fender. The large connector contains the self test output (STO) and ground
(SIG RTN). The small pigtail is the self test input (STI).
Click on the image to enlarge
1. Make sure engine is fully warmed. If in
doubt, run engine at 2000 rpm for 2 minutes.
2. Turn ignition off and wait 10 seconds for system to shut off. Make sure A/C is off and
transmission is in Park (automatic) or Neutral (manual).
3. Hook up light and jumper (or a tester if you have one). Turn key to ON (do not start
engine).
4. Fast Codes are output (ignore fast light flashes).
5. Read hard faults.
6. Separator Pulse.
7. Read memory codes.
8. See code explanations and check components as necessary.
Use FIRST CODE OUTPUT and retest after any repairs are made.
KEY ON ENGINE RUNNING (KOER) TEST
1. Make sure engine is fully warmed. If in
doubt, run engine at 2000 rpm for 2 minutes.
2. Turn ignition off and wait 10 seconds for system to shut off. Make sure A/C is off and
transmission is in Park (automatic) or Neutral (manual).
3. Hook up light and jumper (or tester if you have one).
4. Make sure vehicle is safe to run and start engine.
5. Engine I.D. should be output.
6. Step on brake and turn steering wheel 1/4 turn.
7. If a "Goose" pulse is received, move throttle quickly 1/2 way down and
release.
8. Fast Codes are output (ignore).
9. Read codes.
10. See code explanations and check components as necessary.
Use FIRST CODE OUTPUT and retest after any
repairs are made.
CYLINDER BALANCE TEST
NOTE: This test is only available on
Sequential Fuel Injection (SFI) Engines.
Start an engine running test and press the accelerator lightly within 2 minutes after the
last code is output. The PCM will cancel each cylinder in turn and measure the RPM drop.
If any weak cylinders are noted their number will be output as a multiple of 10 (e.g. 30,
40). The output is the actual cylinder number, not the number in the firing order. NOTE:
Will not always pinpoint bad injectors.
WIGGLE TEST
Engine running or engine off tests
Hook up for a self test but do not hook up the self test trigger. Turn key to on. Hook up
the trigger, wait 10 seconds and disconnect. Hook up trigger again . Tap suspected sensors
(be careful if engine is running), wiggle the wiring harnesses etc. IF the PCM picks up a
fault the self test output will pulse and a memory code will be stored (The value of this
is questionable. I NEVER located a problem with it. - JT).
MEMORY ERASE
To erase the memory disconnect the self test
trigger while the codes are being output. You COULD also disconnect the battery but then
the PCM forgets some important running characteristics.
OUTPUT STATE TEST
Run the KOEO test all the way through and
leave the test hooked up.
Cycle throttle 3/4 open and closed while watching tester, light or voltmeter. Self test
output will switch with every throttle activation. On some testers (like my old pocket
testers) the light will only pulse every other push. But the outputs still switch EVERY
time.
Solenoids (EGR etc.) will switch on or off with every throttle activation (push throttle
they're on, push throttle they're off). You should be able to hear clicks as the solenoids
switch states. The test will work for most solenoids: AIRB, AIRD, BOOST, EGR, EVR (NOTE:
EVR does not click but vacuum cycles).
2 Digit Codes - 3 Digit Codes
Some information, and pictures courtesy of Dali Design
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your car or to yourself while working on your car. You work on your car at your
own risk. If you don't know you can do this yourself, bring it to a mechanic who
can.
Any modifications, repairs or maintenance can be very dangerous, so be careful!
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