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Cam Sensor Hard Failure

Old 08-20-2015, 09:57 AM
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Default Cam Sensor Hard Failure

Had my first Camshaft Position Sensor failure. Hard fail - in my driveway (luckily). Replaced it with my spare out of my spare distributor.


What I found interesting was when cranking the engine in the start attempt, the CHECK ENGINE light illuminated while cranking and went out when I released the key to RUN. With the key in RUN there was no CEL. Tried it again and got the CEL during crank.


Hooked up my scanner to check for codes/pending codes - none found.


I changed the CMP as a hunch. Engine started right up, but the CEL was on so I checked it. The code was P0340 - No Cam Signal at PCM! Cleared the code and it has been off since. The CMP was the original OEM CMP - lasted 138,000 miles and 16 years.


What I wanted to point out here (for future reference) is that I got a CEL while cranking, but no CEL when not cranking. Something for folks to look for with a "No Start" problem.


As a side note: My '99 diagnostics manual states, for P0340, the set condition is "If 96 crank signals are counted and no signal from the cam position sensor is present the code will set." I'm assuming that the 96 crank signals is referring to the Crankshaft Position Sensor signals. There are three sets of 'windows' in the flex plate that trigger CPS signals, each set counted as one signal. If this is the case. it would take 32 rotations of the flex plate to complete the 96 crank signals. No wonder I didn't get a CEL after a few start attempts (only during cranking though).
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Old 08-20-2015, 11:39 AM
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Very interesting. Thanks for posting this.
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Old 08-20-2015, 12:14 PM
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That post got me to thinking about something I've often wondered about with these OBD systems. I really do like having the ability to check for tripped codes w/o a scanner. But I've only ever had a code tripped and the CEL come on together once and it was my fault as I had unknowingly disconnected the IAC while tightening the T/B. The only other code besides that one was for the CTS but the CEL never came on. I recently replaced both o2 sensors after a trip I'd made and had gotten under 15mpg. Fixed the situation but no codes or CEL were ever seen. My understanding is that in order for the CEL to come on a certain number of criteria must be met for each circuit the OBD monitors. Don't know why that is but maybe if it wasn't designed that way the CEL would be activated too easily. So what I do is periodically check the OBD for tripped codes.
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Old 08-20-2015, 08:07 PM
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Good stuff, Ken.

This forum needs a "Thank you for this useful post." button. I've seen it on other forums that use vBulletin.
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