DTC P0172 Fuel Trim System Rich. Pontiac Sunfire 2000

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 2000 🢒 Sunfire 🢒 DTC 🢒 DTC P0172 Fuel Trim System Rich

System Description

A Closed Loop air/fuel metering system is used to provide the best possible combination of driveability, fuel economy, and emission control. While in a Closed Loop operation, the Powertrain Control Module (PCM) monitors the oxygen sensor signal voltage and adjusts the fuel delivery based on the signal voltage. The long-term fuel trim values and the short-term fuel trim values can indicate any changes to the fuel delivery. Monitor the scan tool for these changes. The ideal fuel trim value is approximately 128, or 0 percent. If the oxygen sensor signal indicates a lean condition, the PCM will add fuel, resulting in fuel trim values more than 128, that is, from 0 percent to 100 percent. If you detect a rich condition, the fuel trim values will be less than 128, or from 0 percent to -100 percent, indicating that the PCM is reducing the amount of fuel delivered. If the exhaust emissions reach an excessive level due to a lean or a rich condition, a fuel trim DTC is set.

Conditions for Running the DTC

•	DTCs P0105, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0201, P0202, P0203, P0204, P0300, P0325, P0335, P0341, P0342, P0446, P0502, P0503, P0506, P0507, P0601, P0602, P1133, and P1441 are not set.

•	The intake air temperature (IAT) is between -25°C (-13°F) and 115°C (175°F).

•	The engine coolant temperature is between 60°C (140°F) and 115°C (239°F).

•	The engine speed is between 550 RPM and 3400 RPM.

•	The vehicle speed is below 116 km/h (72 mph).

•	The MAP is more than 26 kPa.

•	The BARO is more than 72 kPa.

•	The EVAP purge is not occurring.

Conditions for Setting the DTC

•	The fuel trim index is less than 70 (-46 percent).

•	The above condition is present for more than 16 seconds.

Action Taken When the DTC Sets

•	The malfunction indicator lamp (MIL) will illuminate if the fault is active within the same conditions for two out of 80 ignition cycles.

•	The MIL will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.

•	The PCM will record the operating conditions at the time that the diagnostic fails. This information will store in the Freeze Frame and Failure Records buffers.

•	A history DTC will store.

•	The coolant fan turns ON.

Conditions for Clearing the MIL/DTC

•	The MIL turns OFF after three consecutive ignition cycles during which the diagnostic runs without a fault present under the Freeze Frame conditions that existed when the DTC failed.

•	A history DTC clears after 40 consecutive warm up cycles without a fault.

•	Use a scan tool to clear the DTCs.

Diagnostic Aids

Important: After repairs, use the scan tool Fuel Trim Reset function in order to reset the long term fuel trim to 128 (0 percent).

•	Check for a faulty electrical connection at the PCM. Inspect the harness connectors for the following conditions:

-	Backed-out terminals

-	Improper mating

-	Broken locks

-	Improperly formed electrical connectors

-	Damaged terminals

-	A faulty terminal-to wire-connection

•	Inspect the wiring harness for damage. If the harness appears to be OK, observe the O2S 1 display on the scan tool while moving the electrical connectors and the wiring harness related to the engine harness. A change in the display will indicate the location of the malfunction.

•	Check for a contaminated crankcase.

•	Check for a restricted intake manifold.

•	Check for a restricted exhaust system.

•	A shorted 5 volt reference circuit may cause a DTC P0172 to set. Check the 5 volt reference sensors for abnormal readings.

Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the Freeze Frame and Failure Records data on the scan tool, if applicable. This creates an electronic copy of the data that was captured when the malfunction occurred. The scan tool stores this data for later reference.

A more negative value indicates the PCM is leaning the fuel mixture, a rich condition. A more positive value indicates the PCM is richening the fuel mixture, a lean condition.

This step checks for a fuel delivery concern.

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 other than P0172, refer to those DTCs before proceeding with this diagnostic.

Install the scan tool.
Idle the engine in closed loop at the normal operating temperature.
Use the scan tool to monitor the long-term fuel trim (FT).

Is the long-term FT value closer to 0% than it is to the specified value?

--14 %

Go to Step 3

Go to Step 4

Turn ON the ignition, leaving the engine OFF.
Review the Freeze Frame and Failure Records for this DTC and observe the parameters.
Turn OFF the ignition for 15 seconds.
Start the engine.
Operate the vehicle within the conditions for this diagnostic to run, and as close to the conditions recorded in Freeze Frame or Failure Records as possible.
Select DTC and the Specific DTC function.
Enter the DTC number which was set.

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

Go to Step 4

Go to Diagnostic Aids

Visually and physically check the following items:

•	The air filter for being restrictions

•	The air intake duct for being collapsed or restricted

•	The IAC, if a low or unsteady idle is being experienced

•	Check for throttle body coking or for objects blocking the IAC passages.

•	Check the O2S 1 electrical connector for contact with the exhaust system.

•	Check the fuel pressure regulator for proper operation or a slow diaphragm leak. Refer to Fuel System Diagnosis .

•	Check for excessive fuel in the crankcase. Change the oil if necessary.

Did any of the above checks isolate a condition requiring repair?

Go to Step 9

Go to Step 5

Turn OFF the ignition.
Turn ON the ignition, leaving the engine OFF.
The fuel pump should run for approximately 2 seconds.
It may be necessary to cycle the ignition ON more than once in order to obtain maximum pressure.
Monitor the fuel pressure with the fuel pump running. The fuel pressure should be within the first specified value range.
When the fuel pump stops, the fuel pressure may vary slightly, then it should hold steady within the second value range.

Is fuel pressure within the specified value ranges and does it hold?

248-325

kPa (41-47 psi)

Go to Step 6

Go to Step 12

Perform the Fuel Injector Balance Test .

Did you find an injector problem?

Go to Step 10

Go to Step 7

Perform the Evaporative Emission Control System Diagnosis .

Did you find a problem?

Go to Step 8

Go to Diagnostic Aids

Repair the EVAP system.
Use the Fuel Trim Reset function on the scan tool.
Operate the vehicle in Closed Loop while monitoring the long-term FT display.
The long-term FT should increase above the specified value.

Is the long-term FT value closer to 0% than to the specified value?

-14 %

Go to Step 11

Go to Step 4

Repair the items found in Step 4.
Use the Fuel Trim Reset function on the scan tool.
Operate the vehicle in Closed Loop while monitoring the long-term FT display.
The long-term FT value should increase above the specified value.

Is the long-term FT value closer to 0% than the specified value?

-14 %

Go to Step 11

Go to Step 5

Replace the fuel injector. Refer to Fuel Injector Replacement .
Use the Fuel Trim Reset function on the scan tool.
Operate the vehicle in Closed Loop while monitoring the long-term FT display.

The long-term FT value should increase above the specified value.

Is the long-term FT value closer to 0% than the specified value?

-14 %

Go to Step 11

Go to Step 5

A rich condition is not present. Does a driveability symptom still exist?

Go to Symptoms

Go to Step 13

Refer to Fuel System Diagnosis .

Is the action complete?

Go to Step 13

Using the scan tool, clear the DTCs.
Start the engine.
Select DTC and the Specific DTC function.
Enter the DTC number which was set.
Operate the vehicle, with the Conditions for Setting this DTC, until the scan tool indicates the diagnostic Ran.

Does the scan tool indicate the diagnostic passed?

Go to Step 14

Go to Step 2

Does the scan tool display any additional undiagnosed DTCs?

Go to Diagnostic Trouble Code (DTC) List/Type

System OK