DTC P0172

DTC P0172  : Fuel System Too Rich

Special Tools Required 

Vacuum Pump/Gauge, 0-30 inHg Snap-on YA4000A or equivalent, commercially available 

NOTE: 

• Before you troubleshoot, 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 is 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, troubleshoot those DTCs first, then recheck for P0172.

  P0010, P0011, P100A, P100B, P100C, P100D: VTC system

  P006A, P0101, P0102, P0103: MAF sensor

  P0105, P0106, P0107, P0108: MAP sensor

  P0130, P0133, P2195, P2237, P2238, P2243, P2245, P2251, P2252, P2A00: A/F sensor (Sensor 1)

  P0134, P0135: A/F sensor (Sensor 1) heater

  P0137, P0138, P0139, P2270, P2A01: Secondary HO2S (Sensor 2)

  P0141: Secondary HO2S (Sensor 2) heater

  P0201, P0202, P0203, P0204: No. 1 - No. 4 cylinder injector (s)

  P0400, P0401, P0404, P0405, P0406, P046C, P049D, P2413: EGR system

  P0443, P04AB: EVAP canister purge valve

  P2279: Intake air leakage

  P2646, P2647, P2648, P2649: VTEC system

DTC (PGM-FI)

1. Problem verification - Idle

   -1. Enter the maintenance mode, then start the engine .

   -2. Hold the engine speed at 3, 000 rpm without load (in P or N) until the radiator fan comes on, then let it idle.

   -3. Check the parameter (s) below with the HDS.

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   AF FB (ST Fuel Trim)	Less than 0.79

   Do the current condition (s) match the threshold?

   YES 

   The AF FB (ST FUEL TRIM) is too low at idle. Go to step 3.

   NO 

   The AF FB (ST FUEL TRIM) is OK at idle. Go to step 2.

2. Problem verification - On-board Snapshot

   -1. Review the on-board snapshot and record the value of the parameters below when AF FB (ST FUEL TRIM) was at its lowest point.

   Engine Speed
   Vehicle Speed
   REL TP Sensor
   APP Sensor

   On-board Snapshot

   -2. Drive the vehicle according to the conditions determined above.

   Signal	Current conditions
   	Values	Unit
   Engine Speed
   Vehicle Speed
   REL TP Sensor

   Signal	Current conditions
   	Values	Unit
   APP Sensor

   -3. With the help of an assistant, check the parameter (s) below with the HDS while driving.

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   AF FB (ST Fuel Trim)	Less than 0.79

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

   YES 

   AF FB (ST FUEL TRIM) is too low under the conditions above. Go to step 3.

   NO 

   AF FB (ST FUEL TRIM) is OK under the same conditions as the on-board snapshot. The system is normal at this time. If the on-board snapshot of this DTC is recorded, try to reproduce the failure under the same conditions with the on-board snapshot .

3. Check fuel pressure

   -1. Enter the maintenance mode, then start the engine , and let it idle.

   -2. Check the fuel pressure under the conditions when AF FB (ST FUEL TRIM) is 0.79 or less.

   Signal	Current conditions
   	Values	Unit
   AF FB (ST Fuel Trim)

   Is the fuel pressure within a specified range of fuel pressure test ?

   YES 

   The fuel pressure is OK. Go to step 4.

   NO 

   Replace the fuel pressure regulator and the fuel tank unit .

4. 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. Turn the vehicle to the OFF (LOCK) mode.

   -2. Drain the fuel from the fuel tank unit, and refill the fuel tank with known-good fuel.

   -3. Enter the maintenance mode, then start the engine , and let it idle.

   -4. Operate the vehicle under the same conditions where AF FB (ST FUEL TRIM) was 0.79 or less.

   Engine Speed
   Vehicle Speed
   REL TP Sensor
   APP Sensor

   On-board Snapshot

   Signal	Current conditions
   	Values	Unit
   Engine Speed
   Vehicle Speed
   REL TP Sensor
   APP Sensor

   -5. With the help of an assistant, check the parameter (s) below with the HDS while driving.

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   AF FB (ST Fuel Trim)	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 AF FB (ST FUEL TRIM) value. Go to step 5.

   NO 

   The fuel was causing the low AF FB (ST FUEL TRIM) value.

5. Check MAF sensor reading

   -1. Continue to let the engine idle.

   Make sure the following conditions are met:

   • ECT Sensor 1 above 158 deg.F (70 deg.C)
   • Transmission in P or N
   • 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.

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   MAF Sensor	7.5-10.5	g/s

   Do the current condition (s) match the threshold?

   YES 

   The MAF sensor read value 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 MAF sensor/IAT sensor 1 .

6. Check engine oil

   -1. Continue to let the engine idle.

   -2. Gently pinch the PCV hose (A).

   Courtesy of HONDA, U.S.A., INC.

   -3. Check the parameter (s) below with the HDS with the PCV hose pinched.

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   AF FB (ST Fuel Trim)	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. Check EVAP canister purge valve

   -1. Turn the vehicle to the OFF (LOCK) mode.

   -2. Disconnect the following connectors.

   EVAP canister purge valve 1 2P connector

   EVAP canister purge valve 2 2P connector

   -3. Disconnect the vacuum hose (purge line) (A) from the 3-way joint (B) in the engine compartment, and connect a vacuum pump/gauge, 0-30 inHg to the 3-way joint as shown.

   Courtesy of HONDA, U.S.A., INC.

   -4. Enter the maintenance mode, then start the engine , and let it idle.

   Is there vacuum?

   YES 

   When the climate is warm, fuel vapor from the canister line to the fuel tank enters intake manifold, enriching mixture (excessively rich), causing the engine to stall in some cases. If needed, replace EVAP canister purge valve 1 and/or EVAP canister purge valve 2 .

   NO 

   Go to step 8.

8. Replace A/F sensor (Sensor 1)

   -1. Turn the vehicle to the OFF (LOCK) mode.

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

   -3. Enter the maintenance mode, then start the engine , and let it idle.

   -4. Operate the vehicle under the same conditions where AF FB (ST FUEL TRIM) was 0.79 or less.

   Engine Speed
   Vehicle Speed
   REL TP Sensor
   APP Sensor

   On-board Snapshot

   Signal	Current conditions
   	Values	Unit
   Engine Speed
   Vehicle Speed
   REL TP Sensor
   APP Sensor

   -5. With the help of an assistant, check the parameter (s) below with the HDS while driving.

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   AF FB (ST Fuel Trim)	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 AF FB (ST FUEL TRIM) value. Reinstall the original A/F sensor (Sensor 1), then go to step 9.

   NO 

   The A/F sensor (Sensor 1) was causing the low AF FB (ST FUEL TRIM) value. Replace the original A/F sensor (Sensor 1) .

9. Replace injectors

   -1. Turn the vehicle to the OFF (LOCK) mode.

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

   -3. Enter the maintenance mode, then start the engine , and let it idle.

   -4. Operate the vehicle under the same conditions where AF FB (ST FUEL TRIM) was 0.79 or less.

   Engine Speed
   Vehicle Speed
   REL TP Sensor
   APP Sensor

   On-board Snapshot

   Signal	Current conditions
   	Values	Unit
   Engine Speed
   Vehicle Speed
   REL TP Sensor
   APP Sensor

   -5. With the help of an assistant, check the parameter (s) below with the HDS while driving.

   Signal	Threshold		Current conditions
   	Values	Unit	Values	Unit
   AF FB (ST Fuel Trim)	Less than 0.79

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

   YES 

   The injectors are not the cause of the low AF FB (ST FUEL TRIM) value. Substitute a known-good PCM , then recheck.

   NO 

   The injectors were causing the low AF FB (ST FUEL TRIM) value. Replace the original injectors .