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In the infancy of the automobile, nearly every control system was placed right in or around the carburetor, with various jets, valves, and the choke all right in one place. With computer-controlled carburetors and, later, computer-controlled fuel injection, systems were dispersed throughout the engine bay (and right inside the passenger compartment) as more and more factors were monitored and controlled. With more information and faster reactions, computers could deliver better-targeted amounts of air and fuel and time spark plugs to fire exactly when needed; computers could also control turbochargers for efficiency, power, driveability, and durability.
By programming the computer to understand what to expect, and to record error codes when unexpected things happened, Chrysler engineers also provided technicians and owners with excellent diagnostic tools that the best mechanics of the carburetor era could only dream of. What’s more, to prevent damage (and to let the owner know something was seriously wrong), the computer could even send the car into “limp home” mode, providing a reasonable level of performance until repairs were made — while some competitors let their customers thumb a ride.
Bob O’Neill and Bob Lincoln have written most of the following pages, which describe individual systems, switches, sensor, and the like. This is a work in progress and will be added to. Many of the pages are focused on the 2.2 and 2.5 liter engines used throughout the 1980s and up until 1994, but similar systems existed on many other engines — including those made today. (Chrysler dropped mechanical distributors and switched from a “MAP” based system to a “MAF” based system in the 1990s, and to a CAN based electronics system in the 2000s, but many sensors and systems remained.)
MD Butler wrote...
My son-in-law had been driving this 2005 PT Cruiser non-turbo... He had some problem with it ... I read these codes:
I added a fuel line schraeder valve to check pressure; pressure was at the top of the range.
I replaced the MAP sensor (unnecessarily) because it read 0.485Volts which should have been between 4 and 5V although the 5V “reference” was good. Swapping the MAP changed nothing, so from that point I took my time learning and diagnosing.
I found 14 ohms resistance from the block to the fender and negative battery terminal. Before redoing all of those I looked at the computer connections. It had been to the beach I could tell from a bit of the fine sand. There was some fine surface corrosion on some of the pins (salt water and even beach air is corrosive). I cleaned them with a plastic brush and contact cleaner, CRC I think. That or some other fiddling apparently improved my block to ground resistance because it went away.
Looking at the bigger picture, most or all of the codes implied a 5V problem, I would have thought the supply, but that was fine in different places. Finally, I decided to pull all of the sensors involved, one-by-one to see if one was pulling the MAP output down from an internal short to ground.
My MAP 5V reference (green as I recall) still reading 5V reference OK. I connected the meter to the MAP signal (orange as I recall) still read 0.485V.
Well, here I go pulling the connectors, Cam Position Sensor was easy to get to so it was first and BAM, sensor voltage went up to 4.8 Volts. Got the new Cam Position Sensor installed and she cranked right up.
The important learning here to me is that ... one sensor output can short, pulling other sensors down. That means any of Cam Position Sensor, Crank Position Sensor, Throttle Position Sensor, oil pressure, and whatever else shows in these codes can bring the others down.
A mechanic friend told me of one that was odd with a cam sensor that appeared to be bad but wasn’t. He eventually found a pin that fixed the magnet to the cam for Cam Position Sensor to read had sheared. The magnet piece stayed in place while the cam still rotated until he replaced the pin.
Sensors, Switches, and Other Systems | Main Repairs Page | EEKs
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