No check engine light?

caddy91caddy91 Member Posts: 7
edited January 2016 in Cadillac
How can i see if theres any issues with my engine through the computer in my car?? None of my dash lights are on but how do i know if my engine is messed up or if its over heating?? 88 deville 4.5


  • thecardoc3thecardoc3 Member Posts: 5,696
    edited January 2016
    GM in the late eighties built a scan too, right into the car with their top of the line models. You'll need a service manual to work your way through this but it starts with you turning the key on and then you simultaneously push and hold the "Off" and "Warmer" buttons on the HVAC control head. You will then see the fuel mileage display show you all 8888s, and then it will show you two FF's and a number if there are codes in the body computer, the numbers after the FF's being the code and then two EE's and a number if there are codes in the fuel injection computer.

    Then the fun really starts. It will show you the initials for one of the vehicle modules such as the ECM or BCM with a question mark. If you want to look into the BCM you push the "Hi" blower button while BCM is displayed. Then it will ask you if you want code, data, or bi (for bidirectional controls). When the one you want is displayed you press the "Hi" again and it will take you to that function. Then again using the Hi or lower button will let you scroll through the data or controls depending on what you selected.

    The ECM (engine control module) will work the same way, but there are hundreds of pages of information that you must go through in order to know what data you are looking at, so even though I could describe it nothing will work as good as grabbing a service manual and just doing it.
  • caddy91caddy91 Member Posts: 7
    Okay awesome thank you man!!! Ill tinker with her tonight very good information.... Thanks again
  • caddy91caddy91 Member Posts: 7
    The code said ff. 48 then ended with 7.0... Manual doesntt tell me what that code means
  • caddy91caddy91 Member Posts: 7
    Ff48 and E9.5 or 95 whats that mean?
  • thecardoc3thecardoc3 Member Posts: 5,696
    You will have to get a service manual, study the system in the manual, and then follow it while performing diagnostics. The FF48 is a historical code for the low side AC pressure was too low. If you were actively performing diagnostics with the AC not working correctly and the pressure was low you would only get an F48, with the single F indicating that the condition is current.

    The 7.0 is displayed after codes are displayed indicating that the system is ready for the next command. When you got to E 9.5, you had pushed the "Hi" button while the 7.0 was displayed. That took you to ECM output cycling. If a technician is working on the car and analyzing a given system that the ECM controls. E 9.5 can be entered and now the ECM will keep turning everything that it controls on and off, which allows the technician to analyze a given circuit (system) independent of normal engine operating conditions.

    There are hundreds of pages to this onboard diagnostic system in the service manual. You will have to have the manual and follow it to make sense of it all.
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