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Unread 09-22-2010, 06:18 PM   #1
jarrod318
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Pcm Internal Shutdown Timer Rationality Too Slow

Hello

I just hit 36K and the check engine light came on. The code is P 1607 and when I looked it up it said "PCM internal shutdown time rationality too slow"? Anyone know what that means? Any help is much appreciated.

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Unread 09-22-2010, 06:45 PM   #2
yoda13
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that is a new one on me...my curiosity is piqued...
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Unread 09-22-2010, 06:59 PM   #3
ls6tt
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here you go

Pcm Internal Shutdown Timer Rationality Too Slow - Lone Star Jeep Club
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Unread 09-22-2010, 07:02 PM   #4
jarrod318
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Hmm, interesting.....Looks like I need to stop by the dealership. I was hoping that I could just reset it but it may be more complicated. Thanks for the info Ls6tt.
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Unread 09-22-2010, 07:21 PM   #5
ronjenx
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Some more info for this code:

Theory of Operation



The PCM compares actual shutdown time to a calculated shutdown time value. The calculated shut down time value is based on the amount the ECT should drop after a completely warmed up engine is shut down for a minimum of 8 hours. If the difference between actual shutdown time and the calculated shut down time is greater than a maximum value, a one trip failure will set. The shutdown time is measured again after 1 hour of ignition off time following the next engine warm up cycle. The PCM compares the shutdown time to a calculated value. If the difference is greater than a maximum value, the MIL is illuminated and a DTC will set.

When Monitored:
With the engine running after a cycle when a complete engine warm up was achieved, the difference between engine coolant temperature and ambient air temperature less than or equal to 10° C (50° F), and battery voltage greater than 10 volts.

Set Condition:
This DTC sets if the engine coolant temp does not drop enough or drops too much during engine off time. This DTC may also set if the controller timer is inaccurate. Two Trip Fault. Three good trips to turn off the MIL.

NOTE: This DTC will set if the engine cools quicker than it should compared to engine off times. If the customer washed a hot engine with the engine off, a One Trip Failure will set. If the vehicle is parked in a highly ventilated area or has a large fan blowing on it which might cause the engine to cool quicker than expected this DTC may set.

WARNING: Do not remove or loosen the radiator cap with the system hot and under pressure. Serious burns from coolant can occur.
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Unread 09-22-2010, 07:28 PM   #6
jarrod318
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So the engine is cooling off to quickly? Maybe I should wait a few days before going to the dealership to see if it goes off after a few trips.
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Unread 09-22-2010, 08:09 PM   #7
Boodyrider
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Quote:
Originally Posted by jarrod318 View Post
So the engine is cooling off to quickly? Maybe I should wait a few days before going to the dealership to see if it goes off after a few trips.
No. Your coolant temp sensor is likely bad.
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Unread 09-22-2010, 08:14 PM   #8
ronjenx
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Quote:
Originally Posted by Boodyrider View Post
No. Your coolant temp sensor is likely bad.
That could be. However, it is not mentioned in any of the troubleshooting.

It's an easy and cheap item to change to eliminate that possibility.

I don't see why this parameter is even monitored.
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Unread 09-23-2010, 05:10 AM   #9
J_Westy
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Originally Posted by ronjenx View Post
I don't see why this parameter is even monitored.
It's all part of OBD-II. The PCM needs an accurate engine-off timer to run certain diagnostic strategies and obviously the coolant temp sensor needs to work. This DTC says the two don't jive -- i.e. they are not rational relative to each other.
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Unread 09-23-2010, 06:56 AM   #10
DAYJ
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remember when engines use to be simple?
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Unread 09-23-2010, 08:11 AM   #11
jarrod318
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Agreed DAYJ. I am so lost on this one. The waranty just ran out and the dealer wants $120 to just look at it so I may try to change to the temp sensor myself.
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Unread 09-23-2010, 08:29 AM   #12
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Quote:
Originally Posted by J_Westy View Post
It's all part of OBD-II. The PCM needs an accurate engine-off timer to run certain diagnostic strategies and obviously the coolant temp sensor needs to work. This DTC says the two don't jive -- i.e. they are not rational relative to each other.
The reason I was wondering why it is monitored...

It doesn't appear the OBD II can recognize a bad temp sensor.
People with temp sensors that were way off didn't get this code, or any other code. The symptom was the temp gauge was too high or too low, when the actual engine temp was normal. Too high would cause their fan to be on all the time. Too low would prevent their fan from coming on when it should.
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Unread 09-24-2010, 08:21 AM   #13
jarrod318
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Ok, so the check engine light went off by its self? I have read somewhere that it takes 3 cycles to reset the computer.and it was exactly the 3rd time that i have driven her when it went off. Was this just a weird hick up of some sort and is ok now? Guess I have to wait and see...
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Unread 09-24-2010, 02:00 PM   #14
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Glad to see you got it fixed. That was a strange one.
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Unread 09-24-2010, 02:25 PM   #15
tavic
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Possibility of an air bubble triggering it?
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