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Unread 10-04-2011, 08:43 AM   #1
frisbeeguy
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Won't pass inspection - Code PO174

Hi y'all,
I've searched with no luck finding any answers.
Dad's 2004 Grand Cherokee 4.0 inline 6.

Code PO174 (twice)

Replaced both upstream O2 sensors & cleaned intake & cleared code. It came back along with code P1196.

Can anybody tell me what to replace to get this thing to pass emissions testing?

Thanks, frisbeeguy

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Unread 10-04-2011, 09:06 AM   #2
mfalik
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Well, P0174 is "FUEL SYSTEM LEAN" and could have been caused by many things (not just the O2 sensor):

Good trip equal to zero
Restricted fuel supply line
Fuel pump inlet strainer plugged
Fuel pump module
O2 sensor
O2 signal circuit
O2 return circuit
O2 sensor heater operation
MAP sensor operation
ECT sensor operation
Engine mechanical problem
Fuel Filter/pressure regulator (high)
PCM

P1196 is O2 SENSOR 2/1 SLOW DURING CATALYST MONITOR

Exhaust leak
Resistance in the O2 sensor signal circuit
Resistance in the (K4) O2 sensor ground circuit
O2 sensor

My suggestion is to have a mechanic look at it to figure what caused the P0174 code, because it could be a fuel delivery issue.
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Unread 10-04-2011, 09:15 AM   #3
frisbeeguy
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Oh, well thanks Mr. mfalik!
Hmmm, this makes it a bit tougher to fix!

Unfortunately, I'm a dedicated DIY'er. It might cost me more in parts but I get the satisfaction of fixing it. (or scrapping it!!!)

It seems to run O.K. - a bit rough at idle while in gear stopped at a light.
Perhaps a fuel filter will help - cheap & easy.
I'll find a repair manual for reference.

Ant thougts on what order I should check on the above listed potential causes?

Thanks again -
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Unread 10-04-2011, 09:16 AM   #4
frisbeeguy
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BTW... what do you mean by: "Good trip equal to zero" ?
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Unread 10-04-2011, 10:14 AM   #5
rm2001wj
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From what you posted, it seems replacing upstream sensors got rid of the P0174, but now you have P1196. If I understood you correctly, then the problem now is with 2/1 sensor. The code indicates that sensor is not operating correctly. In order to find out for sure, clear the codes and swap the upstream sensors with each other. If a code P1195 is thrown now, then you will know that the 1/1 sensor is faulty and needs replacement.
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Unread 10-04-2011, 10:36 AM   #6
mfalik
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Quote:
Originally Posted by frisbeeguy View Post
BTW... what do you mean by: "Good trip equal to zero" ?
It's part of the fun world of On Board Diagnostics 2 (OBD II). 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.

Below is a run down of OBD:

Description of On-Board Diagnostics
The PCM is responsible for efficiently coordinating the operation of all the emissions-related components. The PCM is also responsible for determining if the diagnostic systems are operating properly. The software designed to carry out these responsibilities is call the 'Task Manager'.

The Task Manager determines which tests happen when and which functions occur when. 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 know 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 EGR 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 precis diagnosis.

For example, if the PCM is storing a one trip fault for the Oxygen Sensor and the EGR monitor, the Task Manager may still run the EGR 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 EGR 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 third 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 third key cycle) During the key cycle for the third good trip, the Requested MIL state is OFF, while the Actual MILL 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.
•Priority 2 One trip failure of a two trip fault for fuel system (rich/lean) or misfire.
•Priority 3 Two trip failure for a non-fuel system and non-misfire or matured one trip comprehensive component fault.
•Priority 4 Two trip failure or matured fault for fuel system (rich/lean) and misfire or one trip catalyst damaging misfire.

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 speed is within ±375 RPM and load is within ±10% 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 DRB III. Erasing the DTC with the DRB III erases all OBD II information. The DRB III 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:

•Specific Good Trip
•Fuel System Good Trip
•Misfire Good Trip
•Alternate Good Trip (appears as a Global Good Trip on DRB III)
•Comprehensive Components
•Major Monitor
•Warm-Up Cycles

Specific Good Trip
The term Good Trip has different meanings depending on the circumstances:

•If the MIL is OFF, a trip is defined as when the Oxygen Sensor Monitor and the Catalyst Monitor have been completed in the same drive cycle.
•If the MIL is ON and a DTC was set by the Fuel Monitor or Misfire Monitor (both continuous monitors), the vehicle must be operated in the Similar Condition Window for a specified amount of time.
•If the MIL is ON and a DTC was set by a Task Manager commanded once-per-trip monitor (such as the Oxygen Sensor Monitor, Catalyst Monitor, Purge Flow Monitor, Leak Detection Pump Monitor, EGR Monitor or Oxygen Sensor Heater Monitor), a good trip is when the monitor is passed on the next startup.
•If the MIL is ON and any other emissions DTC was set (not an OBD II monitor), a good trip occurs when the Oxygen Sensor Monitor and Catalyst Monitor have been completed, or two minutes of engine run time if the Oxygen Sensor Monitor and Catalyst Monitor have been stopped from running.

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

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 DRB III. 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 160 °F
•Engine coolant temperature must rise by 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 DRB Ill 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 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.
•Misfire Data - Data collected during test.
•Test Done This Trip - Indicates YES when the test is done.
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Unread 10-05-2011, 06:56 AM   #7
frisbeeguy
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Ah ha! - Now that's a mouthful. Many thanks - this will help since good 'ol dad's OCD was in high gear yesterday after paying another $40 and failing emissions again. This after I told him NOT to take it in until I'd exhausted my efforts to remedy the reason it's not passing. (routine maintenance is not done to his vehicles)
He could only focus on the fact there was no MIL "on" (because I cleared the codes to see what comes up next) so it should pass.

Thanks again for the help.
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Unread 10-05-2011, 07:03 AM   #8
frisbeeguy
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Quote:
Originally Posted by rm2001wj View Post
From what you posted, it seems replacing upstream sensors got rid of the P0174, but now you have P1196. If I understood you correctly, then the problem now is with 2/1 sensor. The code indicates that sensor is not operating correctly. In order to find out for sure, clear the codes and swap the upstream sensors with each other. If a code P1195 is thrown now, then you will know that the 1/1 sensor is faulty and needs replacement.
Actually my ability to write & describe the problem & solutions to read clearly are not so good. The PO174 returned after replacing both upstream O2 sensors.
I popped in a new fuel filter yesterday.
Don't know if it'll help but the car has 115,000 miles and as far as I know it is still all original including plugs & sensors. It looked like the stock fuel filter and I'm sure the O2 sensors were the originals.
I ordered a new MAP sensor - it sounds like these seem to need replacing on these vehicles as they are out of stock on the shelf and the warehouse from the local auto parts store and it could also be causing the PO174 code.

My bigger problem is I'll be just like him (dad) at 88 - bull-headed and consumed w/ OCD at times. - yikes!!!!
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