Retrieving the Codes
The easiest way to retrieve diagnostic trouble codes on a Ford is with a scan tool. Fords require opening and closing the self test input (STI) lead at various times; scan tools have much of the diagnostic routine programmed in, and will provide any prompts necessary to walk you through the test procedure.

What’s more, many Fords don’t provide a malfunction indicator lamp to flash out the codes. Very often you have to use an analog voltmeter or some other type of device to read the codes.

Finally, later model Fords use three-digit codes; counting the flashes or voltmeter needle sweeps for code "675" (transmission range sensor voltage out of range) can become awkward at best.

But if a scan tool isn’t available, you can read Ford diagnostic trouble codes without one, using the malfunction indicator lamp (if there is one) or a voltmeter.

Start by locating the self test connector: It’s usually around a shock tower or near the firewall.

The self test connector is actually two connectors: a main connector and a separate pigtail connector. Here’s how to identify the individual terminals:

With the key off, ground the self test input connector—that’s the separate pigtail connector. If the car has a malfunction indicator lamp, that’s all you have to do—turn the key on, engine off, and the lamp will start flashing codes.

But if there’s no malfunction indicator lamp in the car, you’ll need to use something to read the codes. Ford recommends an analog voltmeter for this, but you can use almost anything that displays voltage changes: A digital oscilloscope, test light, or even a beeper will all work to display the codes. We’ll use a voltmeter, but feel free to substitute.

Connect the negative lead of your voltmeter to the self test output terminal. Connect the positive lead to any 12-volt source, such as the positive battery terminal.

Counting the Codes
Now turn the key on, engine off, and the voltmeter needle should start sweeping toward 12 volts.

The time between the flashes or needle sweeps lets you determine whether it’s part of the same digit, a different digit, or a different code. Here’s how to identify the difference:

So here’s how a series of codes will appear:

Here's how to read the codes, base on the on-time and the off-time.

Reading the Codes
Fords display three different types of codes: Two are key on, engine off (KOEO) codes; that is, to read these codes, the key must be on, but the engine off. The other is a key on, engine running (KOER) code. Here are the three different types of codes:

Here’s how to read each code:

On vehicles with diesel engines, you must hold the accelerator pedal to the floor during the KOEO On-Demand and Continuous Memory tests.

KOEO On-Demand Codes: These are the first codes the computer displays during a self test. KOEO On-Demand codes aren’t stored in memory; the computer runs through a quick series of checks, and indicates any problems it recognizes at that moment. If the problem isn’t there right now, it won’t show up during this series. Any codes that display during this series indicate hard faults.

If doesn’t recognize any faults in the system, the computer displays code 11 (or 111 on systems with three-digit codes). This is also called "Pass 11" (or "Pass 111"); it indicates no hard faults in the system.

Separator Code: In between the KOEO On-Demand codes and the KOEO Continuous Memory codes, the system displays a code 10. This appears as a single flash (or sweep), since the computer can’t display a zero. Code 10 tells you there are no more KOEO On-Demand codes in memory, and it’s time to move on to the KOEO Continuous Memory codes. There’s a 6 – 9 second pause before and after separator code 10.

KOEO Continuous Memory Codes: These are the next series of codes; they’re the codes the computer has stored in memory. While they may indicate a problem that’s there now, they may also indicate intermittent failures, or a failure that only appears when the engine’s running, such as a vacuum leak.

If there are no codes in memory, the computer again displays a "Pass 11" (or "Pass 111") code.

If you’re using a scan tool, you may have to wait up to 15 seconds for the system to display its Continuous memory codes. Give it time: If you disconnect the scan tool before it’s finished displaying the codes, the system will erase the codes before you have a chance to read them.

KOER On-Demand Codes: Once you’ve read the KOEO On-Demand and Continuous Memory codes, your next step is to check for problems that only show up while the engine’s running. These problems appear as KOER On-Demand codes. Since they’re on-demand codes, they don’t store in memory. And they indicate problems that only show up when the engine’s running.

For example, a vacuum leak to the MAP sensor may affect transmission operation, but it won’t show up during the Continuous Memory codes. And since there’s no vacuum when the engine’s off, it won’t show up during the KOEO self test either.

Here’s how to check the KOER On-Demand Codes:

Here’s what you’ll see:

Engine ID Code: The first thing the computer will do is to send the Engine ID code. This code should be a series of pulses, equal to half the number of cylinders in the engine. So a four cylinder engine will receive two pulses, a six cylinder receives three pulses, and an eight cylinder receive four pulses.

Technician Intervention
As soon as the system displays the cylinder ID, you’re going to have to perform a few quick procedures:

Now there will be a long pause — maybe as long as 20 seconds.

Dynamic Response Test: At this point, some systems will require a Dynamic Response Test. The computer examines the sensor response when you goose the throttle.

Watch for a single pulse: That’s dynamic response code 10. If you see this single pulse, goose the throttle quickly, all the way to the floor, and release it.

Some systems won’t require a dynamic response test. They’ll skip ahead to the next step.

Now the needle on your voltmeter may wiggle a bit. That’s the computer sending its fast codes; these are the codes a scan tool would read. Ignore them.

Six seconds after the computer delivers its fast codes, it begins pulsing out the KOER On-Demand Codes. Remember, these are the codes that won’t remain in memory; any problem that only shows up while the engine is running should appear in these codes.

If the computer doesn’t identify any problems, it’ll display a Pass 11 code.

Computed Timing Test: You can stop here, but at this point the computer fixes the timing at about 20° before top dead center. This allows you to check the timing, to make sure the computer is controlling it properly.

Power Balance Test: Finally, on vehicles with sequential fuel injection, the system goes into a power balance test. This enables the computer to identify weak cylinders in the engine.

To end this test mode, shut the key off and disconnect the ground lead to the self test input terminal.

The Wiggle Test
As One of the biggest problems you’re likely to run into is loose connections. Most manufacturers have a continuous harness, from the computer connector to the inputs and outputs, to prevent connection problems.

Not Ford. Most Fords have dozens of connectors, with short pieces of harness between them. This enables Ford to use the same harness for many different cars and trucks. But it also presents the possibility of a loose connection causing a computer system problem.

That’s why Ford builds a special test mode into their computer systems: the wiggle test. The procedure is simple: You put the computer into a special mode, where it looks for momentary glitches, and then wiggle the harness, shake the connectors, tap on sensors and switches. You can even apply heat to components, to see if they have a problem after they get hot.

KOEO Wiggle Test
There are two types of wiggle test: engine off and engine running. The engine running test actually lets you drive the car, to look for problems that only show up while driving. Here are the procedures for entering and performing the wiggle tests:

Now work your way around the wiring harness, wiggling the wires and connectors. Tap gently on the sensors and outputs. If you suspect a temperature-related problem, apply heat to the components or connectors with a hair dryer or heat gun.

If the computer sees any problems during this test, the needle on your meter will wiggle slightly. That indicates the computer stored a code in memory. Go back and check the KOEO Continuous Memory codes.

KOER Wiggle Test
Another type of wiggle test you can perform is to check the system with the engine running. This "key on, engine running" wiggle test lets you stress the components and circuits under actual driving conditions. So this test can be very useful for isolating hard-to-find component and circuit failures.

Here’s how to perform the KOER wiggle test:

Now go for a drive; try to duplicate the conditions that cause the problem in the first place. Hard acceleration, quick deceleration, hard turns — whatever condition seemed to cause the problem. When the problem occurs, the needle on your meter should wiggle slightly; if the vehicle has a MIL, it’ll flash. Check the KOEO Continuous Memory codes to determine the source of the problem.

Output State Test
There’s one more test you may want to perform during your Ford diagnostic checks: the output state test. During this test, you can turn nearly all of the computer-controlled solenoids and relays on and off, just by pressing and releasing the gas pedal.

The output state test occurs right after the computer system finishes displaying the KOEO Continuous Memory codes. As soon as the Continuous Memory codes are finished, press the gas pedal to the floor and release it. That puts the system into the output state mode. Nearly all of the computer outputs should be energized — including the transmission shift solenoids.

Now you can check the circuits, to make sure they’re energized, and check the solenoids, to make sure they’re working. This is also a good time to think about Ohm’s Law: Volts ÷ Ohms = Amps. So if you know the solenoid resistance spec, you can determine whether the solenoid is okay by measuring its current draw.

For example, if the solenoid should have 10 ohms resistance, the formula would be:

12.6 ÷ 10 = 1.26

…so the solenoid should be drawing 1.26 amps of current. If the solenoid’s drawing much more than that, it’s probably shorted. If it’s drawing much less, it’s probably open.

Press the gas pedal again, and the computer outputs turn off. You can turn the outputs on and off as many times as you want, to determine whether they’re working properly or not.

Clearing the Codes
The procedure for clearing the codes from memory on Fords is simple: Just disconnect the ground lead to the self test input terminal while the system is displaying diagnostic trouble codes. The computer will erase any codes it has stored automatically.

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