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How to get trouble codes from 1988 to 1995 Ford trucks without expensive equipme

Self-test connctor and self-test input 1989 Ford Bronco
Self-test connctor and self-test input 1989 Ford Bronco
Art Heberger

Today’s automotive engines are run by an Engine Control Module that receives signals from various sensors located throughout the vehicle. This was true for late-80’s to mid-90’s Ford trucks as well, but to a lesser extent.

The control module – or computer, as some people call it – receives information from the sensors and compares it to the specifications programed by the manufacturer. If possible, the module will then sends signals back to sensors, relays and actuators to make any adjustments based on the information received. When a sensor is defective, and the module receives either no signal or the wrong signal, your engine isn’t going to respond normally and may run rough, stall, or not run at all. The module is programed to perform tests when it doesn’t receive a signal, or receives an out of spec signal. The module will then generate a code based on its findings.

Luckily, there is a way to ask the module what is happening. By counting the flashes of the “Check Engine” light you can retrieve codes from the module, and you don’t need to go out and spend hundreds of dollars on a scanning tool to do it.

This procedure is for 1988 to 1995 Ford pick-up trucks and Broncos equipped with EEC-IV

The only equipment you need is a jumper wire that you will make yourself. You will need:

  • A six inch piece of wire.
  • Two male quick disconnects.
  • A wire stripper/crimper

You may also want to grab a pen and a notebook to write down the codes.

Make the jumper wire

  • Strip both ends of the wire.
  • Crimp one disconnect onto each side of the wire.


  • Check the air cleaner ducts for proper installation.
  • Check for damaged, crimped, missing or misrouted vacuum lines.
  • Check the module, sensors and actuators for any signs of damage.
  • Check all fluid levels.
  • Turn off all accessories.


  • Look on the fender well under the master cylinder. You will find the self-test connector and the self-test input – see picture. Check both for any damage or loose wires.
  • Start your engine.
  • Run it until it reaches operating temperature.
  • Shut it down.

Key On Engine Off Self-Test

  • Turn the ignition key to the on position.
  • Connect your jumper wire from the Signal Return pin on the self-test connector (see picture) to the self-test input.
  • Watch for the “Check Engine” light to begin flashing. It should take between 15 and 45 seconds, and you will hear clicking noises from the engine as the module does its tests.
  • Count the flashes and record the codes.
  • When the flashes end, turn off the key and disconnect the wire.

Engine Running self-test

  • Start your engine.
  • Run it 2000 rpm for two minutes.
  • Shut it down and wait 10 seconds.
  • Start your engine.
  • Connect your jumper wire from the signal return pin on the self-test connector (see picture) to the self-test input.
  • Watch for the ID code:
  1. Four flashes – 8 cylinder
  2. Three flashes – 6 cylinder
  • If equipped with Brake On/Off Switch, depress and release the brake pedal.
  • If equipped with Power Steering Pressure Switch, turn the steering wheel at least one-half turn and release it.
  • If you get a Dynamic Response Code – one single flash of the Check Engine light – push the throttle wide-open and release it.
  • Count the flashes and record the codes.

Depending on the year and problem, you will get a two or three digit code. There will be a two second pause between digits and a four second pause between codes.

For example, on a 1990 full size Bronco, you could see:
Four flashes, a two second pause, two flashes, a four second pause, three flashes, a two second pause, eight flashes. You have a code 42 and a code 38.

Once you have the codes, you can ask a local parts store to look it up for you, check their website, look it up yourself in a repair manual, or a website like this one -- Actron

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