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Unread 09-11-2009, 11:48 AM   #1
ChillyWillys
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Engine Light Staying On - Owners Manual Useless!!

I noticed this morning that my engine warning light on the instrument panel is now staying on while the vehicle is moving. I pulled over and stopped and then pulled out the owners manual. Among other things it said: “Certain conditions, such as a loose or missing gas cap, poor fuel quality etc, may illuminate the light after engine start. The vehicle should be serviced if the light stays on through several of your typical driving cycles. In most situations the vehicle will drive normally and will not require towing.”

That was the middle paragraph of three on pg. 181 of my manual. After reading all three paragraphs I said to myself: “So tell me something that I don’t already know!” I’m not a mechanic; but this was still all pretty mundane stuff; if you ask me. For the hell of it, I checked the gas cap (as instructed) and I also checked all the fittings under the hood that I could get to; and everything was as it should be. I know the fuel quality is fine because I don’t use “garbage gas”. I’ve always been told that when any of these warning lights stay on they’re on for a reason. I just thought the manual could have offered a bit more in the way of useful information. I talked to my dealer and they said that: “It could be a million things that are causing it to stay lit.”

If any of you can offer up any ideas of what any of the “millions of things” might be that could be causing this, I’d appreciate hearing from you.

Thanks!

Bill

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Unread 09-11-2009, 12:38 PM   #2
wesleyd
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Originally Posted by ChillyWillys View Post
I noticed this morning that my engine warning light on the instrument panel is now staying on while the vehicle is moving. I pulled over and stopped and then pulled out the owners manual. Among other things it said: “Certain conditions, such as a loose or missing gas cap, poor fuel quality etc, may illuminate the light after engine start. The vehicle should be serviced if the light stays on through several of your typical driving cycles. In most situations the vehicle will drive normally and will not require towing.”

That was the middle paragraph of three on pg. 181 of my manual. After reading all three paragraphs I said to myself: “So tell me something that I don’t already know!” I’m not a mechanic; but this was still all pretty mundane stuff; if you ask me. For the hell of it, I checked the gas cap (as instructed) and I also checked all the fittings under the hood that I could get to; and everything was as it should be. I know the fuel quality is fine because I don’t use “garbage gas”. I’ve always been told that when any of these warning lights stay on they’re on for a reason. I just thought the manual could have offered a bit more in the way of useful information. I talked to my dealer and they said that: “It could be a million things that are causing it to stay lit.”

If any of you can offer up any ideas of what any of the “millions of things” might be that could be causing this, I’d appreciate hearing from you.

Thanks!

Bill
Until you get a scanner to read the code you won't know what caused it. Every sensor or computer malfunction will make the light come on. Unfortunately the only way to see what it was is to use a scanner. Some parts places will scan for free but if its still under warranty you should take it to the dealer. There isn't quite a million things that can cause this but there are several hundred. Most common are loose gas cap, bad seal on gas cap, faulty O2 sensor. Even though you may not buy "garbage gas" the vendor doesn't know the state of the fuel when it gets delivered by truck, or for that matter the vendor most likely doesn't know the state of his own tanks.
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Unread 09-11-2009, 01:37 PM   #3
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You asked!

OPERATION
The Task Manager determines when tests happen and when functions occur. Many of the diagnostic steps required by OBD II must be performed under specific operating conditions. The Task Manager software organizes and prioritizes the diagnostic procedures. The job of the Task Manager is to determine if conditions are appropriate for tests to be run, monitor the parameters for a trip for each test, and record the results of the test. Following are the responsibilities of the Task Manager software:

Test Sequence
MIL Illumination
Diagnostic Trouble Codes (DTCs)
Trip Indicator
Freeze Frame Data Storage
Similar Conditions Window

Test Sequence
In many instances, emissions systems must fail diagnostic tests more than once before the PCM illuminates the MIL. These tests are known as 'two trip monitors.' Other tests that turn the MIL lamp on after a single failure are known as 'one trip monitors.' A trip is defined as 'start the vehicle and operate it to meet the criteria necessary to run the given monitor.'

Many of the diagnostic tests must be performed under certain operating conditions. However, there are times when tests cannot be run because another test is in progress (conflict), another test has failed (pending) or the Task Manager has set a fault that may cause a failure of the test (suspend).

Pending
Under some situations the Task Manager will not run a monitor if the MIL is illuminated and a fault is stored from another monitor. In these situations, the Task Manager postpones monitors pending resolution of the original fault. The Task Manager does not run the test until the problem is remedied.

For example, when the MIL is illuminated for an Oxygen Sensor fault, the Task Manager does not run the Catalyst Monitor until the Oxygen Sensor fault is remedied. Since the Catalyst Monitor is based on signals from the Oxygen Sensor, running the test would produce inaccurate results.

Conflict
There are situations when the Task Manager does not run a test if another monitor is in progress. In these situations, the effects of another monitor running could result in an erroneous failure. If this conflict is present, the monitor is not run until the conflicting condition passes. Most likely the monitor will run later after the conflicting monitor has passed.

For example, if the Fuel System Monitor is in progress, the Task Manager does not run the catalyst Monitor. Since both tests monitor changes in air/fuel ratio and adaptive fuel compensation, the monitors will conflict with each other.

Suspend
Occasionally the Task Manager may not allow a two trip fault to mature. The Task Manager will suspend the maturing of a fault if a condition exists that may induce an erroneous failure. This prevents illuminating the MIL for the wrong fault and allows more precise diagnosis.

For example, if the PCM is storing a one trip fault for the Oxygen Sensor and the catalyst monitor, the Task Manager may still run the catalyst Monitor but will suspend the results until the Oxygen Sensor Monitor either passes or fails. At that point the Task Manager can determine if the catalyst system is actually failing or if an Oxygen Sensor is failing.

MIL Illumination The PCM Task Manager carries out the illumination of the MIL. The Task Manager triggers MIL illumination upon test failure, depending on monitor failure criteria.

The Task Manager Screen shows both a Requested MIL state and an Actual MIL state. When the MIL is illuminated upon completion of a test for a good trip, the Requested MIL state changes to OFF. However, the MIL remains illuminated until the next key cycle. (On some vehicles, the MIL will actually turn OFF during the thirdgood trip) During the key cycle for the third good trip, the Requested MIL state is OFF, while the Actual MIL state is ON. After the next key cycle, the MIL is not illuminated and both MIL states read OFF.

Diagnostic Trouble Codes (DTCs) With OBD II, different DTC faults have different priorities according to regulations. As a result, the priorities determine MIL illumination and DTC erasure. DTCs are entered according to individual priority. DTCs with a higher priority overwrite lower priority DTCs.

Priorities
Priority 0 —Non-emissions related trouble codes.
Priority 1 — One trip failure of a two trip fault for non-fuel system and non-misfire. (MIL Off)
Priority 2 — One trip failure of a two trip fault for fuel system (rich/lean) or misfire. (MIL Off)
Priority 3 — Two trip failure for a non-fuel system and non-misfire or matured one trip comprehensive component fault. (MIL On)
Priority 4 — Two trip failure or matured fault for fuel system (rich/lean) and misfire or one trip catalyst damaging misfire. Catalyst damage misfire is a 2 trip MIL. The MIL flashes on the first trip when catalyst damage misfire levels are present. (MIL On)
Non-emissions related failures have no priority. One trip failures of two trip faults have low priority. Two trip failures or matured faults have higher priority. One and two trip failures of fuel system and misfire monitor take precedence over non-fuel system and non-misfire failures.

DTC Self Erasure
With one trip components or systems, the MIL is illuminated upon test failure and DTCs are stored.

Two trip monitors are components requiring failure in two consecutive trips for MIL illumination. Upon failure of the first test, the Task Manager enters a maturing code. If the component fails the test for a second time the code matures and a DTC is set.

After three good trips the MIL is extinguished and the Task Manager automatically switches the trip counter to a warm-up cycle counter. DTCs are automatically erased following 40 warm-up cycles if the component does not fail again.

For misfire and fuel system monitors, the component must pass the test under a Similar Conditions Window in order to record a good trip. A Similar Conditions Window is when engine RPM is within ±375 RPM and load is within ±20% of when the fault occurred.

NOTE: It is important to understand that a component does not have to fail under a similar window of operation to mature. It must pass the test under a Similar Conditions Window when it failed to record a Good Trip for DTC erasure for misfire and fuel system monitors.

DTCs can be erased anytime with a scan tool. Erasing the DTC with the scan tool erases all OBD II information. The scan tool automatically displays a warning that erasing the DTC will also erase all OBD II monitor data. This includes all counter information for warm-up cycles, trips and Freeze Frame.

Trip Indicator The Trip is essential for running monitors and extinguishing the MIL. In OBD II terms, a trip is a set of vehicle operating conditions that must be met for a specific monitor to run. All trips begin with a key cycle.

Good Trip

The Good Trip counters are as follows:

Global Good Trip
Fuel System Good Trip
Misfire Good Trip
Alternate Good Trip (appears as a Global Good Trip on scan tool)
Comprehensive Components
Major Monitor
Warm-Up Cycles
Global Good Trip

To increment a Global Good Trip, the Oxygen sensor and Catalyst efficiency monitors must have run and passed, and 2 minutes of engine run time.

Fuel System Good Trip

To count a good trip (three required) and turn off the MIL, the following conditions must occur:

Engine in closed loop
Operating in Similar Conditions Window
Short Term multiplied by Long Term less than threshold
Less than threshold for a predetermined time
If all of the previous criteria are met, the PCM will count a good trip (three required) and turn off the MIL.

Misfire Good Trip

If the following conditions are met the PCM will count one good trip (three required) in order to turn off the MIL:

Operating in Similar Condition Window
1000 engine revolutions with no misfire
Alternate Good Trip

Alternate Good Trips are used in place of Global Good Trips for Comprehensive Components and Major Monitors. If the Task Manager cannot run a Global Good Trip because a component fault is stopping the monitor from running, it will attempt to count an Alternate Good Trip.

The Task Manager counts an Alternate Good Trip for Comprehensive components when the following conditions are met:

Two minutes of engine run time, idle or driving
No other faults occur
The Task Manager counts an Alternate Good Trip for a Major Monitor when the monitor runs and passes. Only the Major Monitor that failed needs to pass to count an Alternate Good Trip.

Warm-Up Cycles

Once the MIL has been extinguished by the Good Trip Counter, the PCM automatically switches to a Warm-Up Cycle Counter that can be viewed on the scan tool. Warm-Up Cycles are used to erase DTCs and Freeze Frames. Forty Warm-Up cycles must occur in order for the PCM to self-erase a DTC and Freeze Frame. A Warm-Up Cycle is defined as follows:

Engine coolant temperature must start below and rise above 71° C (160° F)
Engine coolant temperature must rise by 4.5° C (40° F)
No further faults occur

Freeze Frame Data Storage
Once a failure occurs, the Task Manager records several engine operating conditions and stores it in a Freeze Frame. The Freeze Frame is considered one frame of information taken by an on-board data recorder. When a fault occurs, the PCM stores the input data from various sensors so that technicians can determine under what vehicle operating conditions the failure occurred.

The data stored in Freeze Frame is usually recorded when a system fails the first time for two trip faults. Freeze Frame data will only be overwritten by a different fault with a higher priority.

CAUTION: Erasing DTCs, either with the scan tool; or by disconnecting the battery, also clears all Freeze Frame data.

Similar Conditions Window
The Similar Conditions Window displays information about engine operation during a monitor. Absolute MAP (engine load) and Engine RPM are stored in this window when a failure occurs. There are two different Similar conditions Windows: Fuel System and Misfire.

FUEL SYSTEM

Fuel System Similar Conditions Window — An indicator that 'Absolute MAP When Fuel Sys Fail' and 'RPM When Fuel Sys Failed' are all in the same range when the failure occurred. Indicated by switching from 'NO' to 'YES'.
Absolute MAP When Fuel Sys Fail — The stored MAP reading at the time of failure. Informs the user at what engine load the failure occurred.
Absolute MAP — A live reading of engine load to aid the user in accessing the Similar Conditions Window.
RPM When Fuel Sys Fail — The stored RPM reading at the time of failure. Informs the user at what engine RPM the failure occurred.
Engine RPM — A live reading of engine RPM to aid the user in accessing the Similar Conditions Window.
Adaptive Memory Factor — The PCM utilizes both Short Term Compensation and Long Term Adaptive to calculate the Adaptive Memory Factor for total fuel correction.
Upstream O2S Volts — A live reading of the Oxygen Sensor to indicate its performance. For example, stuck lean, stuck rich, etc.
SCW Time in Window (Similar Conditions Window Time in Window) — A timer used by the PCM that indicates that, after all Similar Conditions have been met, if there has been enough good engine running time in the SCW without failure detected. This timer is used to increment a Good Trip.
Fuel System Good Trip Counter — A Trip Counter used to turn OFF the MIL for Fuel System DTCs. To increment a Fuel System Good Trip, the engine must be in the Similar Conditions Window, Adaptive Memory Factor must be less than calibrated threshold and the Adaptive Memory Factor must stay below that threshold for a calibrated amount of time.
Test Done This Trip — Indicates that the monitor has already been run and completed during the current trip.

MISFIRE

Same Misfire Warm-Up State — Indicates if the misfire occurred when the engine was warmed up (above 71° C (160° F)).
In Similar Misfire Window — An indicator that 'Absolute MAP When Misfire Occurred' and 'RPM When Misfire Occurred' are all in the same range when the failure occurred. Indicated by switching from 'NO' to 'YES'.
Absolute MAP When Misfire Occurred — The stored MAP reading at the time of failure. Informs the user at what engine load the failure occurred.
Absolute MAP — A live reading of engine load to aid the user in accessing the Similar Conditions Window.
RPM When Misfire Occurred — The stored RPM reading at the time of failure. Informs the user at what engine RPM the failure occurred.
Engine RPM — A live reading of engine RPM to aid the user in accessing the Similar Conditions Window.
Adaptive Memory Factor — The PCM utilizes both Short Term Compensation and Long Term Adaptive to calculate the Adaptive Memory Factor for total fuel correction.
200 Rev Counter — Counts 0–100 720 degree cycles.
SCW Cat 200 Rev Counter — Counts when in similar conditions.
SCW FTP 1000 Rev Counter — Counts 0–4 when in similar conditions.
Misfire Good Trip Counter — Counts up to three to turn OFF the MIL.
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Unread 09-11-2009, 01:42 PM   #4
Gramps
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Seriously though. I've had this once in my Compass and once in the Wife's '03 Grand. Mine went out after the next fill up and the wife's went out after the second fill up. You can try to pull the codes, mine didn't send one and the wife's indicated a minor evap leak but nothing that I could find. Unless it flashes don't panic.
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Unread 09-11-2009, 06:06 PM   #5
ChillyWillys
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"Wes" & Bob,

Thanks for the information gentlemen!

"Wes" - As far as taking it to my dealer and having them run a scan to find out what the problem is (if there really is one), they are a 17 mile drive each way from where I live. So I won't be driving over there just to find out that it could indeed just be because of a loose gas cap (or what ever) or nothing at all.

Bob - I'm not panicking. The manual also said that if it isn't flashing I'm OK.
I was just trying to find out what might cause this. Regarding all that info you sent me, I imagine that you have that all saved someplace so all you have to do is a "copy & paste" into the forum here. Either way the thought is appreciated!

Bill
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Unread 09-11-2009, 06:08 PM   #6
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Originally Posted by ChillyWillys View Post
"Wes" & Bob,

Thanks for the information gentlemen!

"Wes" - As far as taking it to my dealer and having them run a scan to find out what the problem is (if there really is one), they are a 17 mile drive each way from where I live. So I won't be driving over there just to find out that it could indeed just be because of a loose gas cap (or what ever) or nothing at all.
Is there an advanced auto or something near by they will do it for free...
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Unread 09-11-2009, 06:31 PM   #7
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"Skip"

I hadn't thought about something like that. There's a Midas Muffler and a Jiffy Lube shop in the next town. They might also be willing to do it. I'll check them out for future reference. Thanks for the thought!

Bill
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Unread 09-11-2009, 06:43 PM   #8
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Quote:
Originally Posted by ChillyWillys View Post
Regarding all that info you sent me, I imagine that you have that all saved someplace so all you have to do is a "copy & paste" into the forum here. Either way the thought is appreciated!

Bill
No Bill, I type a lot! I hate to leave anything out. When I do that turns out to be the cure. It's better to give too much info than not enough. When the MIL light goes out has a lot to do with the "Trip" indicator/counter, you may have fixed it and don't even know it until you have enough "trips". I'd give it another fill up or two before I got concerned.

You can try pulling them yourself.

Retrieving codes:

Turn the ignition key until the digital odometer displays, repeat three times in succession and then back to "On" (On/Off, On/Off, On/Off, On). At the fourth "On" the odometer will be replaced with codes. If no codes are present then "Done" will appear.

or for more info go here: Jeep Grand Cherokee WJ - Diagnostic Trouble Codes
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Unread 09-12-2009, 10:14 AM   #9
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Duplicate Post

Last edited by ChillyWillys; 09-12-2009 at 10:16 AM.. Reason: Duplicate Post
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Unread 09-12-2009, 10:15 AM   #10
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Gramps said: "No Bill, I type a lot! ......"

Oh sure you do! If you think I'm gonna believe that, I have a nice bridge to sell you in the Arizona desert! But all that info you sent still deserves a big THANK YOU!!

However, concerning that last little bit of information in your post above, I assume that’s all true if you have the “high end” version of the OBD II. I don’t. I just have the “plain vanilla” version and can’t access the codes myself. I know this because I remember reading someplace in the manual (that I can’t find right now) that if your odometer does not display the compass directions, you can’t get at the codes yourself. But that’s OK. I’ll keep it all for future reference anyway.

BTW - The problem has already fixed itself!

Thanks again!

Bill
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Unread 09-12-2009, 11:58 AM   #11
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If that's the London Bridge at Lake Havasu? I'll take it! I'm just trying hard not to be a grumpy old man all of the time. You can call me "Walter".

I had no idea that the EVIC display was tied into the OBII. I'll need to look into that.

It fixed itself? I'm not surprised at all.
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Unread 09-12-2009, 02:18 PM   #12
ChillyWillys
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I had no idea that the EVIC display was tied into the OBII. I'll need to look into that.
It may not be. I guess I just assumed that they worked hand in hand with each other. Maybe they don't! Like I said in my post above - the problem fixed itself anyway. So don't loose any sleep over it.

And once more - Thanks!

Bill

Last edited by ChillyWillys; 09-12-2009 at 02:37 PM..
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Unread 09-13-2009, 01:10 PM   #13
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Quote:
Originally Posted by Gramps View Post
If that's the London Bridge at Lake Havasu? I'll take it! I'm just trying hard not to be a grumpy old man all of the time. You can call me "Walter".

I had no idea that the EVIC display was tied into the OBII. I'll need to look into that.

It fixed itself? I'm not surprised at all.
Gramps, ever see Jeff Dunham??? Walter, LOL!!!
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Unread 09-13-2009, 02:12 PM   #14
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Never heard of him!
walter.jpg  
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