Hello, I have an 88 f150 that I would like to read the engine fault codes from. Can someone please explain where to find the diagnostic plug, the terminals to use, and the procedure for reading the codes?

 

The self test plug is on the driver's side inner fender. There is a mess of wires connected to different relays and such, and one little plastic cover is marked "EEC TEST" (I think). There is one big connector with five or six wires and one little one wire connector that pull out the bottom of the cover. Run the vehicle to operating temperature, shut off and wait ten seconds. On the big connector, there is a row of four pins and a row of two. With the connector facing you, and the row of two on top, connect a jumper from the top right pin to the little one wire connector. Turn the key on but do not start the engine, watch the "CHECK ENGINE" light. It will flash faintly and then start flashing the codes. Count how many times it flashes. They will be two or three digit codes seperated by a two second pause between digits, and seperate codes by a four second pause. These first batch of codes are KOEO (Key On Engine Off) codes. Then there will be a 8 or 9 second pause, one flash, another 8 or 9 second pause, then it will flash continous memory codes. These are codes stored from the last 40 or so times the engine was run. They will be displayed in the same format. Make sure the tranny is in park (auto) or neutral (manual) and all electrical loads are off (heater, radio, etc.) before you perform the test.
Then there is the engine running test. Disconnect the jumper and run the engine at 2000 rpm for two minutes, shut it off hook the self test jumper back up, and then restart the engine. If you have a six cylinder, the "CHECK ENGINE" light will flash 3 times, and 4 times for a V-8. If you have an E4OD tranny, mash and release the brake pedal after the engine identification, then turn the steering wheel a half turn then back again to test the power steering pressure switch. If you see a quick flash on the "CHECK ENGINE" light, mash the trottle briefly to perform a wide open trottle test, but don't do it unless you see the light flash. Then it will flash flash the codes.
To erase the codes in memory, begin the KOEO test again, and remove the jumper in the middle of the test. Hope this helps, and good luck.

 

Thank you. I followed your instructions and they worked perfectly. Had a bit of fun finding the plug though. My truck is a right hand drive vehicle exported to Australia. I found the plug behind the left hand cylinder head. I did the test and got the following fault codes. Firstly on the key on engine off, I got a code 11. Then on the engine running I got codes 12,41,13 and 25.
The next question is what do these mean. Is there somewhere that I can get a list of codes??

This site is fantastic, information on F trucks is hard to get in Australia because there are not a lot of them around, all those Japanese 4wd's dominate . Anyway thanks again for the help, it is appreciated.

I bought my truck to drag our trailer around, when I got it I could not get the wife to drive it, I explained that once you get used to the size of the thing that it is a rweally great vehicle to drive. She kicked and bucked a bit, but finally I got her to drive it. Boy what a mistake, I hardly get a go at driving it now. She calls it her truck, the cheek!!!!!

Funny how it is mine again when it needs a wash.

 

11- system pass
12- cannot control rpm, high rpm check
13- cannot control rpm, low rpm check
41- hego sensor (O2 sensor) indicates lean
25- no or little response from knock sensor

I use the Haynes automotive repair manual more than anything else because I can understand what they are saying. My father-in-law lets me borrow his Ford diagnostic manual, but its way over my head. Haynes has most of the codes listed and how to check the related sensors. Codes 12 and 13 are related to the IDLE AIR CONTROL SOLENOID. The OXYGEN sensor has an electric heater with it because it produces no voltage below 600 degrees. If your engine was not fully warmed, or the heater doesn't work this would come back as a lean condition. If you can get a repair manual it will show you how to ckeck each component. Good luck. I don't blame your wife for wanting to drive pick-up all the time, it's almost a religious experience to get to drive a Ford! It helps me get out of bed every morning knowing I get to drive mine. Good Luck Partner.

 

Try these links
http://dalidesign.com/hbook/eectest.html
http://dalidesign.com/hbook/2digit.html
http://dalidesign.com/hbook/3digit.html

Your truck should use the 2 digit format, I think that they changed to the 3 digit in the early 90's.

 

Always run the engine diagnostics with the engine at normal operating temp . For instance if the O2 Sensor is not up to its usable temp it will show up as defective .