Codes 512, 998, 157

1slow5.0h · Dec 1, 2013

Koeo code 512 keep alive memory test fail, what does this mean??

Koer codes 998 hard fail, 157 maf below minimum voltage. What could cause the hard fault code??? Could code 157 be caused by a bad wire or sumtin? Because I replaced the maf already.

95 gt

jrichker · Dec 6, 2013

Did you disconnect the battery for 5 minutes after replacing the sensor? If not, you still have the code present in memory.

Code 15 or 512 - No Keep Alive Memory power to PCM pin 1 or bad PCM (Memory Test
Failure). The voltage to the Keep Alive Memory (KAM) is missing (wiring problem)
or the KAM is bad. The KAM holds all of the settings that the computer "learns" as
it operates and all the stored error codes that are generated as a result of
something malfunctioning while the engine is running. Use a voltmeter to check
the voltage to the pin 1 on the computer - you should always have 12 volts. No
constant 12 volts = bad wiring. If you do always have the 12 volts, then the KAM is
bad and the computer is faulty.

If the computer has to "relearn" all the optimum settings every time it powers up,
the initial 5-30 minutes of operation may exhibit surges, poor low speed performance,
and rough idle.

Note that some aftermarket chips will cause code 15 to set. Remove the chip,
clear the codes and retest.

Before replacing the computer, remove the battery ground cable for about 20
minutes. This will clear all the codes. Retest after several days of running. If the 15
code is gone, then don't worry about it. If it is still there, then you get to do some
troubleshooting.

See the following website for some help from Tmoss (diagram designer) & Stang&2
Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

Diagrams courtesy of Tmoss & Stang&2birds

88-91 5.0 Mustang