Check Engine Light on- Codes P0171 and P0174

[SanDiegoXLR]

Hi All, My check engine light came on, and I used a diagnostic tool to determine the codes triggering it are: P0171 and P0174 (see below). If I clean the mass air flow sensor, will this help clear the codes? Or do I really have to bring it in to the Cadillac dealership to have them Reprogram the Powertrain Control Module (PCM)? Does the emissions warranty cover this work? My car was originally bought Feb 2005 and has 79,000 miles. [url]https://www.xlr-net.com/forums/cadillac-xlr-technical-discussion/4881-check-engine-light-after-cold-start.html For vehicles reprogrammed under the 8 year/80,000 mile (130,000 km) emission controller warranty[/URL] Thanks, Mark ​ Primary DTC: P0171​

Stored DTCs: P0174, P0171

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Freeze Frame Data for Code:	P0171
Parameter	Results
Fuel System 1 Status	Closed Loop
Fuel System 2 Status	Closed Loop
Calculated LOAD Value	26.27 %
Engine Coolant Temp	215.60 °F
Short Term Fuel Trim - Bank 1	10.94 %
Long Term Fuel Trim - Bank 1	15.63 %
Short Term Fuel Trim - Bank 2	7.03 %
Long Term Fuel Trim - Bank 2	15.63 %
Intake Manifold Absolute Pressure	10.96 inHg
Engine RPM	686.00 rpm
Vehicle Speed Sensor	0.00 mph
Ignition Timing Advance #1 Cylinder	12.00 °
Intake Air Temperature	89.60 °F
Air Flow Rate Mass Air Flow Sensor	0.81 lb/min
Absolute Throttle Position	12.16 %
Time Since Engine Start	3024 sec
Commanded Evaporative Purge	0.39 %
Fuel Level Input	94.51 %
Barometric Pressure	28.43 inHg
Control Module Voltage	13.60 V
Absolute Load Value	19.22 %
Commanded Equivalence Ratio	1.00
Relative Throttle Position	1.57 %
Ambient Air Temperature	69.80 °F
Absolute Throttle Position B	12.16 %
Accelerator Pedal Position D	18.43 %
Accelerator Pedal Position E	9.02 %
Commanded Throttle Actuator	2.35 %

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Monitor Name	Status
MIL (Check Engine Light)	ON
Misfire Monitoring	Completed
Fuel System Monitoring	Completed
Comprehensive Component Monitoring	Completed
Catalyst Monitoring	Completed
Evaporative System Monitoring	Completed
Oxygen Sensor Monitoring	Completed
Oxygen Sensor Heater Monitoring	Completed

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CarMD® Validated Most Likely Repair(s)
CarMD has identified 1 most likely repair(s) solutions based on the vehicle's PCM data, VIN information, and reported mileage. All recommended repairs are procured from CarMD’s network of thousands of Automotive Service Excellence (ASE)-certified technicians who input and validate all recommended repair solutions. Parts costs are based on O.E. MSRP and labor costs are based on regional labor rates. For more information on how CarMD collects its data, please visit us at: CarMD Error Page
SOLUTION #1 : Highest probability to repair the problem.
Recommended Repair:	Reprogram Powertrain Control Module (PCM)
Part(s) Required	Unit Cost	Quantity	Total
Labor Required
Root Cause Analysis (in hrs.)*	$75.00	1	$75.00
Technician Repair Time (in hrs.)	$107.17	1hrs.	$107.17
Miscellaneous	$25.00	1	$25.00
Sub-Total Parts Cost =	$0.00
Sub-Total Labor Cost =	$207.17
TOTAL ESTIMATED REPAIR COST =	$207.17

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<img align="absmiddle"> CarMD® Diagnostic Details
Retrieved Diagnostic Code:	P0171
Technical Definition:	Fuel Trim System Lean (Bank 1
Generic Definition:	This fault code indicates the Fuel System Monitor has detected an error in the vehicle’s Bank 1 fuel trim adjustment program, resulting in an air/fuel mixture that is too “lean.” The vehicle’s computer constantly monitors the air/fuel mixture and adjusts it according to current driving requirements. The vehicle’s computer stores predetermined “reference” values for air/fuel ratio for all possible driving conditions (base fuel trim). If the “actual values” from various sensors do not match the “reference” values for a driving condition, the computer command the proper components to make corrections (fuel trim adjustments). Fuel trim adjustments can be “short term” (STFT) or “long term” (LTFT). For STFT, the vehicle’s computer makes adjustments to the base fuel trim program by adding or subtracting fuel to achieve the optimum air/fuel ratio. For LTFT, the vehicle’s computer makes adjustments to the base fuel trim program based on the average of STFT fuel corrections.
Areas to Inspect - Possible Causes:	Air leaks in intake manifold, exhaust pipes or exhaust manifold Fuel control sensor is out of calibration (ECT, IAT or MAF) Fuel component fault (fuel filter, fuel injector, low fuel pressure) HO2S element is contaminated, deteriorated or has failed
OBD II Monitor Type:	Fuel
Definition:	[h=3]Fuel System Monitor Overview[/h] The Fuel System Monitor is a PCM diagnostic that monitors the Adaptive Fuel Control system. The PCM uses adaptive fuel tables that are continually updated and stored in keep alive memory (KAM) in order to compensate for wear and aging in Fuel system components.Once the PCM determines the correct test conditions and the enable criteria are met (ECT, IAT and MAF values in range and with closed loop enabled), the PCM uses its adaptive strategy to "learn" changes needed to correct a Fuel system that is biased either rich or lean. The PCM accomplishes this task by monitoring the Short Term and Long Term fuel trim values during closed loop operation. [h=3]Long and Short Term Fuel Trim[/h] Short Term fuel trim is a PCM parameter identification (PID) used to indicate Short Term fuel adjustments. This parameter is expressed as a percentage and its range of authority is from -10% to +10%. Once the engine enters closed loop, if the PCM receives a HO2S signal that indicates the A/F mixture is richer than desired, it moves the SHRTFT command into a more negative range to correct for the rich condition.If the PCM detects the SHRTFT is adjusting for a rich condition for too long a time, the PCM will �learn� this fact, and move LONGFT into a negative range to compensate so that SHRTFT can return to a value close to 0%. Once a change occurs to LONGFT or SHRTFT, the PCM adds a correction factor to the injector pulsewidth calculation to adjust for any variations. If the change is too large, the PCM will detect a fault.Note: If a fuel injector or fuel pressure regulator is replaced, do a PCM Reset and then drive the vehicle through the Fuel System Monitor drive pattern to reset the Fuel Control table in the PCM. [h=3]Additional Help for Fuel Trim Trouble Codes[/h] The Fuel Trim readings on a Scan Tool do not always indicate a problem by themselves. However, Fuel Trim readings can be a real asset when attempting to determine the cause of one of these trouble codes, and to determine "where to start testing" to find the cause of an Air/Fuel mixture problem or Fuel System control related fault (i.e., related to a fuel control sensor or solenoid that may have failed).One of the first steps is to determine if the PCM is in "control" of the fuel delivery system. There are several test methods that can be used to make this determination. If the PCM is not in "control" of the Fuel Delivery system, the information in the Fuel Trim Repair Table below can be used to help find the cause of a Fuel Trim problem. [h=3]Fuel Trim Repair Table[/h] HO2S Signal Tailpipe Emissions Fuel Trim Value Logical First Step Rich Input (high O2S voltage) Rich A/F Mixture PCM adding fuel (+ %) Check PCM power and ground circuits for faults Rich Input (high O2S voltage) Rich A/F Mixture PCM subtracting fuel (- %) High fuel pressure, leaking injector(s), air intake is restricted, plugged exhaust (MAP sensor) Rich Input (high O2S voltage) Lean A/F Mixture PCM adding fuel (+ %) Test result not logical as more than one fault is present! Rich Input (high O2S voltage) Lean A/F Mixture PCM subtracting fuel (- %) HO2S is contaminated, or the HO2S Heater power circuit is shorted to the HO2S signal Lean Input (low O2S voltage) Rich A/F Mixture PCM adding fuel (+ %) Exhaust leaks in the manifold or pipes, air injection leaks in front of the HO2S, or the HO2S assembly is contaminated or it has failed Lean Input (low O2S voltage) Rich A/F Mixture PCM adding fuel (+ %) Test result not logical as more than one fault is present! Lean Input (Low O2S voltage) Lean A/F Mixture PCM subtracting fuel (- %) Low fuel pressure, dirty fuel injectors, large vacuum leak, or contaminated MAF sensor Lean Input (Low O2S voltage) Lean A/F Mixture PCM subtracting fuel (- %) Check PCM power and ground circuit for high resistance Lean or Rich Input (i.e., a low or high O2S voltage) Lean or Rich A/F Mixture Short Term Fuel Trim at 0% Engine operating in Open Loop mode or in Limp-In mode - check for any stored trouble codes <thead class="yiv1942993112repair_table_header"> </thead> <tbody> </tbody> [h=3]Freeze Frame Data[/h] The PCM stores the current engine operating conditions at the time a trouble code is set in a special portion of memory called Freeze Frame. This important information can help pinpoint the cause of trouble code. It can be retrieved with an OBD II compatible Scan Tool to help diagnose the problem. [h=3]Fuel System Monitor Repair Verification[/h] An example of how to drive a vehicle to verify the repair of a trouble code related to the Fuel System Monitor on these vehicle applications is shown in the Graphic below.
Repair Verification Process:
<img align="absmiddle">
Retrieved Diagnostic Code:	P0171
Technical Definition:	Fuel Trim System Lean (Bank 1
Generic Definition:	This fault code indicates the Fuel System Monitor has detected an error in the vehicle’s Bank 1 fuel trim adjustment program, resulting in an air/fuel mixture that is too “lean.” The vehicle’s computer constantly monitors the air/fuel mixture and adjusts it according to current driving requirements. The vehicle’s computer stores predetermined “reference” values for air/fuel ratio for all possible driving conditions (base fuel trim). If the “actual values” from various sensors do not match the “reference” values for a driving condition, the computer command the proper components to make corrections (fuel trim adjustments). Fuel trim adjustments can be “short term” (STFT) or “long term” (LTFT). For STFT, the vehicle’s computer makes adjustments to the base fuel trim program by adding or subtracting fuel to achieve the optimum air/fuel ratio. For LTFT, the vehicle’s computer makes adjustments to the base fuel trim program based on the average of STFT fuel corrections.
Areas to Inspect - Possible Causes:	Air leaks in intake manifold, exhaust pipes or exhaust manifold Fuel control sensor is out of calibration (ECT, IAT or MAF) Fuel component fault (fuel filter, fuel injector, low fuel pressure) HO2S element is contaminated, deteriorated or has failed
OBD II Monitor Type:	Fuel
Definition:	[h=3]Fuel System Monitor Overview[/h] The Fuel System Monitor is a PCM diagnostic that monitors the Adaptive Fuel Control system. The PCM uses adaptive fuel tables that are continually updated and stored in keep alive memory (KAM) in order to compensate for wear and aging in Fuel system components.Once the PCM determines the correct test conditions and the enable criteria are met (ECT, IAT and MAF values in range and with closed loop enabled), the PCM uses its adaptive strategy to "learn" changes needed to correct a Fuel system that is biased either rich or lean. The PCM accomplishes this task by monitoring the Short Term and Long Term fuel trim values during closed loop operation. [h=3]Long and Short Term Fuel Trim[/h] Short Term fuel trim is a PCM parameter identification (PID) used to indicate Short Term fuel adjustments. This parameter is expressed as a percentage and its range of authority is from -10% to +10%. Once the engine enters closed loop, if the PCM receives a HO2S signal that indicates the A/F mixture is richer than desired, it moves the SHRTFT command into a more negative range to correct for the rich condition.If the PCM detects the SHRTFT is adjusting for a rich condition for too long a time, the PCM will �learn� this fact, and move LONGFT into a negative range to compensate so that SHRTFT can return to a value close to 0%. Once a change occurs to LONGFT or SHRTFT, the PCM adds a correction factor to the injector pulsewidth calculation to adjust for any variations. If the change is too large, the PCM will detect a fault.Note: If a fuel injector or fuel pressure regulator is replaced, do a PCM Reset and then drive the vehicle through the Fuel System Monitor drive pattern to reset the Fuel Control table in the PCM. [h=3]Additional Help for Fuel Trim Trouble Codes[/h] The Fuel Trim readings on a Scan Tool do not always indicate a problem by themselves. However, Fuel Trim readings can be a real asset when attempting to determine the cause of one of these trouble codes, and to determine "where to start testing" to find the cause of an Air/Fuel mixture problem or Fuel System control related fault (i.e., related to a fuel control sensor or solenoid that may have failed).One of the first steps is to determine if the PCM is in "control" of the fuel delivery system. There are several test methods that can be used to make this determination. If the PCM is not in "control" of the Fuel Delivery system, the information in the Fuel Trim Repair Table below can be used to help find the cause of a Fuel Trim problem. [h=3]Fuel Trim Repair Table[/h] HO2S Signal Tailpipe Emissions Fuel Trim Value Logical First Step Rich Input (high O2S voltage) Rich A/F Mixture PCM adding fuel (+ %) Check PCM power and ground circuits for faults Rich Input (high O2S voltage) Rich A/F Mixture PCM subtracting fuel (- %) High fuel pressure, leaking injector(s), air intake is restricted, plugged exhaust (MAP sensor) Rich Input (high O2S voltage) Lean A/F Mixture PCM adding fuel (+ %) Test result not logical as more than one fault is present! Rich Input (high O2S voltage) Lean A/F Mixture PCM subtracting fuel (- %) HO2S is contaminated, or the HO2S Heater power circuit is shorted to the HO2S signal Lean Input (low O2S voltage) Rich A/F Mixture PCM adding fuel (+ %) Exhaust leaks in the manifold or pipes, air injection leaks in front of the HO2S, or the HO2S assembly is contaminated or it has failed Lean Input (low O2S voltage) Rich A/F Mixture PCM adding fuel (+ %) Test result not logical as more than one fault is present! Lean Input (Low O2S voltage) Lean A/F Mixture PCM subtracting fuel (- %) Low fuel pressure, dirty fuel injectors, large vacuum leak, or contaminated MAF sensor Lean Input (Low O2S voltage) Lean A/F Mixture PCM subtracting fuel (- %) Check PCM power and ground circuit for high resistance Lean or Rich Input (i.e., a low or high O2S voltage) Lean or Rich A/F Mixture Short Term Fuel Trim at 0% Engine operating in Open Loop mode or in Limp-In mode - check for any stored trouble codes <thead class="yiv1942993112repair_table_header"> </thead> <tbody> </tbody> [h=3]Freeze Frame Data[/h] The PCM stores the current engine operating conditions at the time a trouble code is set in a special portion of memory called Freeze Frame. This important information can help pinpoint the cause of trouble code. It can be retrieved with an OBD II compatible Scan Tool to help diagnose the problem. [h=3]Fuel System Monitor Repair Verification[/h] An example of how to drive a vehicle to verify the repair of a trouble code related to the Fuel System Monitor on these vehicle applications is shown in the Graphic below.
Repair Verification Process:
<img align="absmiddle">
Retrieved Diagnostic Code:	P0174
Technical Definition:	System Too Lean (Bank 2)
Generic Definition:	This fault code indicates the Fuel System Monitor has detected an error in the vehicle’s Bank 2 fuel trim adjustment program, resulting in an air/fuel mixture that is too “lean.” The vehicle’s computer constantly monitors the air/fuel mixture and adjusts it according to current driving requirements. The vehicle’s computer stores predetermined “reference” values for air/fuel ratio for all possible driving conditions (base fuel trim). If the “actual values” from various sensors do not match the “reference” values for a driving condition, the computer command the proper components to make corrections (fuel trim adjustments). Fuel trim adjustments can be “short term” (STFT) or “long term” (LTFT). For STFT, the vehicle’s computer makes adjustments to the base fuel trim program by adding or subtracting fuel to achieve the optimum air/fuel ratio. For LTFT, the vehicle’s computer makes adjustments to the base fuel trim program based on the average of STFT fuel corrections.
Areas to Inspect - Possible Causes:	N/A

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[airmike]

Code 171 and 174 sounds like a vacuum leak to me. Does it have an erratic or high idle? I would start looking for a loose hose. Spraying carb cleaner at suspected parts can detect a leak.

 

[SanDiegoXLR]

Thanks for the tip. It previously was showing the P0171 code when I had my K&N filter in, so I swapped back to paper filter and it disappeared for a month.

Hmmm...idle has very minor hesitations, but not too bad.
I'll poke around and see if I can find a loose hose.
-Mark

 

[mark henicle]

my findings for having both P0171 and P0174

My problem started out very intemittent, but showed after a very very wet ride one night. Owners manual says this may happen after driving through puddles. Checked connections at all 4 O2 sensors,no problem found. Local tech suggested loose intake bolts. Checked, wow was he right. Tightened, but problem came back. Eventually vaccum leak was very evident, found elbow at back of intake to pvc piping rotted through. didn't want to remove the intake, but eventually had too, there is a monster clamp around the hose and no bent long nose pliers could remove it. Went to my GM dealer, he advised 14 days to get one from Michigan. Went back to my local tech, he handed me a old spark plug boot, wished me a merry xmas. Installed, problem gone. I looked at my ETC and see there is a metal clip that secures the pvc tubing putting less pressure on the very flexible elbow. Don't know if mine was missing all of it's life or came off at some point.

 

[SanDiegoXLR]

Glad you were able to fix your problem!
Thanks for the helpful advice.
I decided to finally clean my mass air flow sensor, and low and behold- I had a few loose intake bolts.
So hopefully by tightening those and cleaning the MAF, I won't see the check engine line for a long, long time.

What sucks is that my check engine light was off for several months, came on for a few weeks, stopped for a few weeks.
I was just about to head over to get my California DMV smog check and it just popped on today.
Not sure how many cycles of re-starting the engine it will take for the light to come off again?
Having the check engine light on is an automatic "fail" in California. My renewal is due at the end of January, so at least I have a few weeks.....fingers crossed.