Code P0172

Tiny
DT5428
  • MEMBER
  • 2005 GMC ENVOY
  • 4.2L
  • 6 CYL
  • 160,000 MILES
Vehicle started losing power almost felt like driving into a strong head wind. Then next day P0172 fault code came up. Changed mass air flow sensor, cleaned throttle body, check fuel pressure and did the leak down test, and changed upstream O2 sensor to rule out. Motor starts right up hot or cold and idles fine. Does not seem to shift smooth but thinking it’s related to lack of power. Going for vacuum lines next but any other input would be appreciated.
Saturday, April 6th, 2019 AT 7:09 AM

15 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning,

The code is rich running in the fuel mapping.

The most common cause is the purge valve for the emission system.

Roy

DTC P0172

CIRCUIT DESCRIPTION
The powertrain control module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open Loop and Closed Loop. During Open Loop, the PCM determines fuel delivery based on sensor signals, without heated oxygen sensor (HO2S) input. During Closed Loop, the PCM adds HO2S inputs and level of purge to calculate the short and long term fuel trim adjustments. If the HO2S indicates a lean condition, the fuel trim values will be greater than 0 percent. If the HO2S indicates a rich condition, the fuel trim values will be below 0 percent. The short term fuel trim values change rapidly in response to the HO2S voltage signals. The long term fuel trim makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1 The fuel trim diagnostic will conduct a test to determine if a rich failure actually exists or if excessive vapor from the evaporative emission (EVAP) canister is causing a rich condition. This DTC is continuously monitored during engine operation. If the PCM detects an excessively rich condition, DTC P0172 sets.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0172 Fuel Trim System Rich

CONDITIONS FOR RUNNING THE DTC
- DTCs P0013, P0014, P0016, P0068, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0135, P0201-P0206, P0220, P0300, P0301-P0306, P0326, P0327, P0341, P0446, P0483, P0496, P0502, P0503, P0506, P0507, P0601, P0602, P0604, P0606, P0641, P0651, P1133, P1516, P1680, P2101, P2120, P2125, P2135, P2138, P2176 are not set.
- The engine is in a Closed Loop status.
- The engine coolant temperature (ECT) is 60-125°C (140-257°F).
- The intake air temperature (IAT) is -25°C to +150°C (-13°F to +302°F).
- The manifold absolute pressure (MAP) is more than 26 kPa (3.8 psi).
- The vehicle speed is less than 132 km/h (82 mph).
- The engine speed is between 400-5,850 RPM.
- The barometric pressure (BARO) is more than 70 kPa (10.2 psi).
- The fuel level is more than 10 percent.
- DTC P0172 runs continuously when the above conditions are met.

CONDITIONS FOR SETTING THE DTC
- The average long term fuel trim value is below -35 percent.
- The diagnostics have determined that a rich condition was not due to excessive vapor.

ACTION TAKEN WHEN THE DTC SETS
- The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
- The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
- The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
- A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
- A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
- Clear the MIL and the DTC with a scan tool.

DIAGNOSTIC AIDS
- Fuel contamination, such as water and alcohol, will affect the fuel trim.
- The system will go rich if the injectors are supplying too much fuel.
- Using the scan tool, review the Failure Records. If an intermittent condition is suspected, refer to Intermittent Conditions. See: Computers and Control Systems > Initial Inspection and Diagnostic Overview > Intermittent Conditions
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Saturday, April 6th, 2019 AT 7:40 AM
Tiny
DT5428
  • MEMBER
  • 9 POSTS
Replaced emissions purge valve no help. Started up and idled fine but no power and shifting a little rough. Any other ideas before I take it to a shop since I don’t have a higher end scan tool? This is my beater whenever possible I like to figure it out myself but this one has me stumped.
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Sunday, April 7th, 2019 AT 8:36 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Can you check the fuel pressure?

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Can you check the catalytic converter back pressure?

https://www.2carpros.com/articles/how-to-test-a-catalytic-converter

https://www.2carpros.com/articles/engine-has-low-power-output

Roy
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Sunday, April 7th, 2019 AT 8:49 AM
Tiny
DT5428
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Fuel pressure and leak down was good. Trying to find fittings to check back pressure might be easier just to remove the converter no emissions testing here.
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Sunday, April 7th, 2019 AT 10:43 AM
Tiny
DT5428
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  • 9 POSTS
Catalytic converter isn’t plugged. Removed air intake and do know that the butter fly is not opening enough when the engine is revving. The butterfly opens freely by hand.
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Sunday, April 7th, 2019 AT 11:07 AM
Tiny
ASEMASTER6371
  • MECHANIC
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What was the fuel pressure?

Compression would be next. Make sure it has 135-150 in each cylinder.

Roy
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Sunday, April 7th, 2019 AT 2:46 PM
Tiny
DT5428
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  • 9 POSTS
The fuel pressure and the leak down test was one of the first things I did a few weeks ago can’t remember exactly but it was almost 60 PSI and only lost a few PSI during the leak down test and I let it sit for a couple of hours. I have a compression tester which I’ll test but I don’t think it’s the issue. I think I’m going to focus on the throttle body power and feedback but haven’t found the pinout so I can use a multi-meter. You’ll find this humorous my buddy is a engineer for GM I told him I never have an issue with my Fords never mind the fact the Envoy is thirteen years old and I always lease my Fords because of A plan.
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Sunday, April 7th, 2019 AT 4:03 PM
Tiny
DT5428
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The fuel pressure and the leak down test was one of the first things I did a few weeks ago can’t remember exactly but it was almost 60PSI and only lost a few PSI during the leak down test and I let it sit for a couple of hours. I have a compression tester which I’ll test but I don’t think it’s the issue. I think I’m going to focus on the throttle body power and feedback but haven’t found the pinout so I can use a multimeter. You’ll find this humorous my buddy is a engineer for GM I told him I never have an issue with my Fords never mind the fact the Envoy is 13 years old and I always lease my Fords because of A plan.
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Sunday, April 7th, 2019 AT 4:03 PM
Tiny
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I would not blow off a compression issue.

I attached a wire diagram for you of the throttle actuator.

Roy
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Sunday, April 7th, 2019 AT 4:10 PM
Tiny
DT5428
  • MEMBER
  • 9 POSTS
Still fighting have 150psi in all 6 cylinder changed the plugs and MAP sensor. Hate throwing parts I like know my fix.
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Saturday, April 13th, 2019 AT 10:47 AM
Tiny
ASEMASTER6371
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Can you give me the long term trim readings for the O2 sensors?

Roy
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Saturday, April 13th, 2019 AT 1:13 PM
Tiny
DT5428
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Unfortunately no. What I don’t understand is the fault code is bank one running rich but yet the throttle body doesn’t open. Is this to keep you at reduced power? Because of the fault code?
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Saturday, April 13th, 2019 AT 1:29 PM
Tiny
ASEMASTER6371
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No, low power is not from the code. That comes from the throttle actuator or pedal sensor. There is a code associated with that.

Roy
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Saturday, April 13th, 2019 AT 1:38 PM
Tiny
DT5428
  • MEMBER
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I only get the P0172 code.
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Saturday, April 13th, 2019 AT 2:10 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Okay, I need the O2 trim readings.

https://www.2carpros.com/articles/engine-has-low-power-output

Roy
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Saturday, April 13th, 2019 AT 2:15 PM

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