Seville running rough,no codes,bizarre behavior


Asked by OrLackThereof84 Feb 07, 2018 at 12:57 AM about the 2002 Cadillac Seville STS FWD

Question type: Maintenance & Repair

I've got a rough idle, (feels like one cylinder isn't
contributing), no codes but also no Service Engine
light whatsoever...doesn't illuminate during the
bulb check. I get all zeroes running active misfire
counters but when I run it and monitor the History
counters, I got a count of 2 on 5 and 2 on 7 but
after two seconds the numbers reset to 0 even
though these were History counts. Also I get a
gauge cluster message saying something like
"#$TPM Voltage" and the voltage measured at the
battery directly while running ,as well as the
reported voltage PID is very high at 15.1 volts on
startup and 14.7 at lowest. When I shut the engine
off but leave the key On, the voltage PID
immediately drops from ~15 volts to
approximately 8.5 volts. The engine knocks, is
badly down on power, and uses about a quart of oil
every 200-300 miles.... I haven't done a
compression test yet and the PCM refuses to
perform a Cylinder Balance self check, it reports
'waiting for idle speed to stabilize'. Idle speed
fluctuates less than 50rpm.

I'm just utterly disgusted with this car at this point
and I'm leaning towards a diagnosis of bad or
broken rings on one or two cylinders , and....a
faulty module?? What's also strange is that since
this started happening, the entertainment system
presets & settings as well as the Driver 1/2 seat
and steering wheel settings WILL NOT LOSE
MEMORY with the battery completely
disconnected for over 24 hours. When I reconnect
both terminals, every radio station preset, every
driver preference setting that used to reset after a
few minutes of being without 12 volts now holds
memory indefinitely. I'm a mechanic of 12 years
and I've never seen anything like it. Has ANY of this
ever happened to anyone else??

2 Answers


TPM voltage might be "tire pressure monitor" voltage. If so it is time to replace all the tire pressure monitor sensors inside the tires. Probably has one of the Northstar engines. Rebuilding one of those requires someone with experience with them as they are complicated as hell.

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