DTC Troubleshooting: P0172, P0175
DTC P0172: Rear Bank (Bank 1) Fuel System Too Rich
DTC P0175: Front Bank (Bank 2) Fuel System Too Rich
NOTE:
Before you troubleshoot, record all freeze data and any on-board snapshot, and review the general troubleshooting information.
Do not clear the DTC or reset the PCM before beginning this troubleshooting procedure until instructed to clear it. Clearing the DTC or resetting the PCM can delete valuable diagnostic information, even if the on-board snapshot and the freeze data are saved.
Inspect for aftermarket fuel system and engine components before beginning troubleshooting.
If any of the DTCs listed below are stored at the same time as P0172 and/or P0175, troubleshoot those DTCs first, then recheck for P0172 and/or P0175.
P0101, P0102, P0103: MAF sensor
P0107, P0108, P2073, P2074: MAP sensor
P0133, P0153, P1172, P1174, P2195, P2197, P2237, P2238, P2240, P2241, P2243, P2245, P2247, P2249, P2251, P2252, P2254, P2255, P2A00, P2A03: A/F sensor (Sensor 1)
P0134, P0135, P0154, P0155: A/F sensor (Sensor 1) heater
P0137, P0138, P0139, P0157, P0158, P0159, P2270, P2272: Secondary HO2S (Sensor 2)
P0141, P0161: Secondary HO2S (Sensor 2) heater
P0201, P0202, P0203, P0204, P0205, P0206: Injector
P0400, P0401, P0404, P0406, P2413: EGR system
P0443: EVAP canister purge valve
P2279: Intake air leakage
P2646, P2647, P2648, P2649, P2651, P2652, P2653, P2654, P2656, P2657, P2658, P2659: VTEC system

DTC Description
Confirmed DTC
Pending DTC
Freeze Frame
P0172 Rear Bank (Bank 1) Fuel System Too Rich
      
P0175 Front Bank (Bank 2) Fuel System Too Rich
      

1.
Problem verification-Idle:

Problem verification-Idle
?1.
Start the engine, and let it idle without load (A/T in P or N, M/T in neutral).

?2.
Check the parameter(s) below with the HDS.
Signal
Threshold
Current conditions
Values
Unit
Values
Unit
ST FUEL TRIM B1
Less than 0.79
      
ST FUEL TRIM B2
Less than 0.79
      

Do the current condition(s) match the threshold?

     
YES
     
     
     
The ST FUEL TRIM (B1, B2) is too low at idle. Go to step 3.
     
NO
     
     
     
The ST FUEL TRIM (B1, B2) is OK at idle. Go to step 2.
2.
Problem verification-On-board Snapshot:

Problem verification-On-board Snapshot
?1.
Review the on-board snapshot and record the value of the parameters below when ST FUEL TRIM (B1, B2) was at its lowest point.
ENGINE SPEED
  
VEHICLE SPEED
  
REL TP SENSOR
  
APP SENSOR
  


?2.
Drive the vehicle according to the conditions determined above.
Signal
Current conditions
Values
Unit
ENGINE SPEED
    
VEHICLE SPEED
    
REL TP SENSOR
    
APP SENSOR
    

?3.
Check the parameter(s) below with the HDS while driving.
Signal
Threshold
Current conditions
Values
Unit
Values
Unit
ST FUEL TRIM B1
Less than 0.79
      
ST FUEL TRIM B2
Less than 0.79
      

Do the current condition(s) match the threshold under the on-board snapshot conditions?

     
YES
     
     
     
ST FUEL TRIM (B1, B2) is too low under the conditions above. Go to step 3.
     
NO
     
     
     
ST FUEL TRIM (B1, B2) is OK under the same conditions as the on-board snapshot. The system is normal at this time.?
3.
Check fuel pressure:

Check fuel pressure
?1.
Start the engine, and let it idle.

?2.
Check the fuel pressure under the conditions when ST FUEL TRIM (B1, B2) is 0.79 or less.
Signal
Current conditions
Values
Unit
ST FUEL TRIM B1
    
ST FUEL TRIM B2
    

Is the fuel pressure between 410?460 kPa (4.18?4.69 kgf/cm2, 59.5?66.7 psi)?

     
YES
     
     
     
The fuel pressure is not the cause of the low ST FUEL TRIM (B1, B2) value. Go to step 4.
     
NO
     
     
     
4.
Replace fuel:

Replace fuel
NOTE: There is an increased likelihood of a fuel related issue if the rich condition appeared shortly after refueling. The MIL DIST (MIL Distance) value in the DATA LIST in combination with the fuel level may help you make this determination.

?1.
Press the engine start/stop button to select the OFF mode.

?2.
Drain the fuel from the fuel tank, then refill the fuel tank with known-good fuel.

?3.
Start the engine, and let it idle.

?4.
Operate the vehicle under the same conditions where ST FUEL TRIM (B1, B2) was 0.79 or less.
ENGINE SPEED
  
VEHICLE SPEED
  
REL TP SENSOR
  
APP SENSOR
  

Signal
Current conditions
Values
Unit
ENGINE SPEED
    
VEHICLE SPEED
    
REL TP SENSOR
    
APP SENSOR
    

?5.
Check the parameter(s) below with the HDS while driving.
Signal
Threshold
Current conditions
Values
Unit
Values
Unit
ST FUEL TRIM B1
Less than 0.79
      
ST FUEL TRIM B2
Less than 0.79
      

Do the current condition(s) match the threshold under the on-board snapshot conditions?

     
YES
     
     
     
The fuel is not the cause of the low ST FUEL TRIM (B1, B2) value. Go to step 5.
     
NO
     
     
     
The fuel was causing the low ST FUEL TRIM (B1, B2) value.?
5.
Check MAF sensor reading:

Check MAF sensor reading
?1.
Continue to let the engine idle.

?2.
Make sure the following conditions are met:
ECT Sensor 1 above 158 °F (70 °C)
A/T in P or N, M/T in neutral
All engine and electrical loads turned off

Signal
Current conditions
Values
Unit
ECT SENSOR 1
    

?3.
Monitor the ENGINE SPEED in the DATA LIST with the HDS, then hold the engine speed at 2,500 rpm with the accelerator pedal held steady.
Signal
Current conditions
Values
Unit
ENGINE SPEED
    

?4.
While holding the engine speed at 2,500 rpm for 30 seconds, check the parameter(s) below with the HDS.
A/T
Signal
Threshold
Current conditions
Values
Unit
Values
Unit
MAF SENSOR
9.8?13.8
g/s
    

M/T
Signal
Threshold
Current conditions
Values
Unit
Values
Unit
MAF SENSOR
9.7?13.7
g/s
    

Do the current condition(s) match the threshold?

     
YES
     
     
     
The MAF sensor is OK. Go to step 6.
     
NO
     
     
     
The MAF sensor read value is incorrect. Inspect for a cracked, damaged, or incorrectly installed air cleaner assembly. If OK, replace the MAF sensor/IAT sensor.?
6.
Check engine oil:

Check engine oil
?1.
Continue to let the engine idle.

?2.
Gently pinch the PCV vacuum hose (A).


?3.
Check the parameter(s) below with the HDS with the vacuum hose pinched.
Signal
Threshold
Current conditions
Values
Unit
Values
Unit
ST FUEL TRIM B1
Less than 0.79
      
ST FUEL TRIM B2
Less than 0.79
      

Do the current condition(s) match the threshold?

     
YES
     
     
     
The engine oil is OK. Go to step 7.
     
NO
     
     
     
The engine oil is contaminated. Determine the cause of the contaminated oil (faulty injectors, etc.), then replace the engine oil and oil filter.?
7.
Replace A/F sensor (Sensor 1)

Replace A/F sensor (Sensor 1)
?1.
Press the engine start/stop button to select the OFF mode.

?2.
Replace the A/F sensor (Sensor 1) with a known-good sensor.

?3.
Start the engine, and let it idle.

?4.
Operate the vehicle under the same conditions where ST FUEL TRIM (B1, B2) was 0.79 or less.
ENGINE SPEED
  
VEHICLE SPEED
  
REL TP SENSOR
  
APP SENSOR
  

Signal
Current conditions
Values
Unit
ENGINE SPEED
    
VEHICLE SPEED
    
REL TP SENSOR
    
APP SENSOR
    

?5.
Check the parameter(s) below with the HDS while driving.
Signal
Threshold
Current conditions
Values
Unit
Values
Unit
ST FUEL TRIM B1
Less than 0.79
      
ST FUEL TRIM B2
Less than 0.79
      

Do the current condition(s) match the threshold under the on-board snapshot conditions?

     
YES
     
     
     
The A/F sensor (Sensor 1) is not the cause of the low ST FUEL TRIM (B1, B2) value, reinstall the original A/F sensor, then go to step 8.
     
NO
     
     
     
The A/F sensor (Sensor 1) was causing the low ST FUEL TRIM (B1, B2) value. Replace the original A/F sensor (Sensor 1).?
8.
Replace fuel injectors:

Replace fuel injectors
?1.
Press the engine start/stop button to select the OFF mode.

?2.
Replace the fuel injectors with known-good fuel injectors.

?3.
Start the engine, and let it idle.

?4.
Operate the vehicle under the same conditions where ST FUEL TRIM (B1, B2) was 0.79 or less.
ENGINE SPEED
  
VEHICLE SPEED
  
REL TP SENSOR
  
APP SENSOR
  

Signal
Current conditions
Values
Unit
ENGINE SPEED
    
VEHICLE SPEED
    
REL TP SENSOR
    
APP SENSOR
    

?5.
Check the parameter(s) below with the HDS while driving.
Signal
Threshold
Current conditions
Values
Unit
Values
Unit
ST FUEL TRIM B1
Less than 0.79
      
ST FUEL TRIM B2
Less than 0.79
      

Do the current condition(s) match the threshold under the on-board snapshot conditions?

     
YES
     
     
     
The fuel injectors are not the cause of the low ST FUEL TRIM (B1, B2) value. Substitute a known-good PCM, then recheck.?
     
NO
     
     
     
The fuel injectors were causing the low ST FUEL TRIM (B1, B2) value. Replace the original fuel injectors.?