I have a 1989 F 150 with a 4.9 engine 2wd and automatic trans. The check engine light has been on for years but I have ignored it since it runs ok except for a surging idle after warmed up when in park or neutral. The rear abs light and brake light recently came on so I figured I should investigate. The brake problem turned out to be the abs hydraulic unit which I replaced and those lights went out. The check engine light is still on. I tried to pull the trouble codes with an Actron obd I tester from the test port under the hood but the tester light remained on and did not flash any codes. As per my Chiltons manual I also tried to pull the codes by hooking an analog volt meter to the test port but the meter showed 12 volts all the time and the needle did not sweep to indicate codes. I also tried to use the MIL (check engine light) to get the codes as per the Chiltons manual instructions but the light remained on solid and did not flash any codes. Does anyone have any ideas why I cannot get the trouble codes?

 

Go to autoparts store they read codes for free! Not all code readers will read all codes!

 

Auto parts stores do not read older (pre-96) OBD1 vehicles.

Verify that you are properly grounding the STI connector pin before turning on the power to force the PCM into the code output mode. You may need to check the integrity of the wiring from the STI pin back to the PCM.

 

You are correct the auto parts stores don't read pre 96 vehicles I already tried that. You say to check that I am properly grounding the STI pin, on my truck this is a separate pin from the test port. Do you mean that the jumper from the STI pin to the test port pin is grounding the STI pin which causes the codes to flash? Chiltons manual shows only two pins on the test port and the STI pin are used to get the codes using a volt meter and only one pin on the test port and the STI pin are used to get the codes using the check engine light method. What I think you are telling me is that the pin on the test port that I am jumpering to the STI pin should be grounded. Is that correct? Thanks for the info.