DTC P0172 Fuel Trim System Rich Bank 1. Pontiac Firebird 1999

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 1999 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P0172 Fuel Trim System Rich Bank 1

Table 1:

Circuit Description

To provide the best possible combination of driveability, fuel economy, and emission control, a closed loop air/fuel metering system is used. While in closed loop, the PCM monitors the bank 1 HO2S 1 and bank 2 HO2S 1 signals and adjusts fuel delivery based upon the HO2S signal voltages. A change made to fuel delivery will be indicated by the long and short term fuel trim values which can be monitored with a scan tool. Ideal fuel trim values are around 0%; if the HO2S signals are indicating a lean condition the PCM will add fuel, resulting in fuel trim values above 0%. If a rich condition is detected, the fuel trim values will be below 0%, indicating that the PCM is reducing the amount of fuel delivered. If an excessively rich condition is detected on bank 1, the PCM will set DTC P0172. The PCM s maximum authority to control long term fuel trim allows a range between -20% and +20%. The PCM s maximum authority to control short term fuel trim allows a range between -20% and +20%. The PCM monitors fuel trim under various operating conditions (fuel trim cells) before determining the status of the fuel trim diagnostic. The fuel trim cells are as follows:

Cell	Purge ON	Purge OFF
Idle (Cell 0)	X	--
Decel (Cell 1)	--	--
Normal (Cell 2)	X	X
Accel (Cell 3)	X	X
High Flow (Cell 4)	X	--

The vehicle may have to be operated in all of the above conditions (marked with X) before the PCM determines fuel trim status. The amount of fuel trim deviates from 0% in each cell and the amount that each cell is used directly affects whether or not the vehicle must be operated in all of the cells described above to complete the diagnostic.

Important: Some conditions can cause multiple cells to indicate rich

Below are some examples of why a rich condition could exist in the above cells.

•	A saturated EVAP canister - This will affect the purge ON cells.

•	A faulty fuel regulator.

•	Gas in the oil pan.

•	A fuel return restriction.

•	A engine misfire.

•	A faulty fuel injector.

•	A restricted exhaust.

Conditions for Running the DTC

•	No VSS, EST, CKP, CAM, TP, Misfire, Fuel Injector, MAF, O2, MAP, EGR, EVAP, ECT or IAT DTCs are set.

•	Engine coolant temperature between 20°C (68°F) and 110°C (230°F).

•	Intake air temperature is between -18°C (0°F) and 70°C (158°F).

•	Manifold absolute pressure is between 15 kPa and 85 kPa.

•	Throttle angle is steady and less than 90%.

•	Vehicle speed is less than 132 km/h (82 mph).

•	Engine speed is between 600 and 4000 RPM.

•	Baro is greater than 70 kPa.

•	Air flow is between 3 gm/s and 150 gm/s.

Conditions for Setting the DTC

•	Bank 1 Long term fuel trim average is at or near maximum authority of -18% and Bank 1 Short term average fuel trim is at or near maximum authority of -2% of the indicated cells in the Fuel Trim Table.

•	All conditions have been met in the Fuel Trim Cells for greater than 1 second.

Action Taken When the DTC Sets

•	The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.

•	The PCM will store conditions which were present when the DTC set as Freeze Frame and Failure Records data.

Conditions for Clearing the MIL/DTC

•	The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been run and passed.

•	The History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.

•	The DTC can be cleared by using the scan tool.

Diagnostic Aids

Check the following items:

•	Fuel pressure high - The system will go rich if pressure is too high. The PCM can compensate for some increase. However, if fuel pressure is too high, a DTC P0172 and P0175 may set. Refer to Fuel System Pressure Test .

•	Fuel injector(s) faulty - Refer to Fuel Injector Balance Test .

•	Check the EVAP Canister for Fuel Saturation. If the EVAP Canister is full of fuel, check canister control and hoses. Refer to Evaporative Emission Control System Diagnosis .

•	Check for a leaking fuel pressure regulator diaphragm by checking the vacuum line to the fuel pressure regulator for the presence of fuel. If there is fuel in the vacuum line, refer to Fuel System Pressure Test .

•	Fuel in the oil pan - The system will go rich if the large amounts of fuel are purged from the oil pan.

•	Engine misfire - The sill go rich due to the lack of complete combustion.

•	Poor connection at the PCM - Inspect harness connectors for the following conditions:

•	Restricted exhaust - The system could indicate a rich condition. Refer to Restricted Exhaust System Check .

-	Backed out terminals.

-	Improper mating.

-	Broken locks.

-	Improperly formed or damaged terminals.

-	Poor terminal to wire connection.

•	Damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, observe the affected HO2S display on the scan tool while moving connectors and wiring harnesses related to the engine harness. A change in the display will indicate the location of the fault.

Review the Freeze Frame/Fail Records vehicle mileage since the diagnostic test last failed. This may help determine how often the condition that caused the DTC to be set occurs.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

This step determines whether the fault is present.

Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This will isolate when the DTC failed. For an intermittent condition, refer to Symptoms.

If DTC 175 is also set, then both banks are operating rich. Inspect items that would cause both banks to operate rich.

Excessive fuel in the oil will cause DTCs P0172 and P0175 to set at the same time. Remove the PCV valve from the intake manifold and plug with a suitable stopper. Also disconnect the fresh air pipe from the rocker cover and plug using asuitable stopper. If the long term and short term fuel trim values increase, indicates there is fuel in the oil.

DTC P0172 BANK 1 RICH

Step

Action

Value(s)

Yes

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Important: If any DTCs are set, except P0172 and P0175, refer to those DTCs before proceeding with this table.

Idle the engine at the normal operating temperature.
Fuel system in Closed Loop.
With a scan tool, observe the Long Term FT Bank 1 parameter.

Does the scan tool indicate fuel trim more thanthe specified value indicated?

-18 % LT

Go to Step 3

Go to Step 4

Turn ON the ignition, with the engine OFF.
With a scan tool, review and record the Failure Records.
Turn OFF the ignition for 15 seconds.
Start the engine.
Operate the vehicle within the Conditions for Setting the DTC, and as close to the Failure Records conditions as possible.

Does the scan tool indicate that this DTC failed this ignition?

Go to Step 4

Go to Diagnostic Aids

Is DTC P0175 also set?

Go to Step 5

Go to Step 6

Visually/physically inspect the following items:

•	Collapsed air intake duct.

•	The air filter element for being restricted. Refer to Air Cleaner Element Replacement .

•	MAF sensor for being installed in the proper direction and for foreign objects blocking the inlet screen. Refer to Mass Airflow Sensor Replacement .