DTC P0172 Fuel Trim System Rich. Pontiac Sunfire 1995

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 1995 🢒 Sunfire 🢒 DTC 🢒 DTC P0172 Fuel Trim System Rich

System 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 powertrain control module (PCM) monitors the oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. A change made to fuel delivery will be indicated by the long and short term fuel trim values which can be monitored with the scan tool. Ideal fuel trim values are around 128 (0 percent). If the oxygen sensor signal is indicating a lean condition, the PCM will add fuel resulting in fuel trim values above 128 (0-100 percent). If a rich condition is detected, the fuel trim values will be below 128 (0 to -100 percent), indicating that the PCM is reducing the amount of fuel delivered. If exhaust emissions reach an excessive level due to a lean or rich condition, a fuel trim DTC is set.

Conditions for Setting

•	When one or more of the following DTCs P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0200, P0300, P0301, P0302, P0303, P0304, P0341, P0342, P0441, P0502, P0503, P0506, P0507, P0600, P1114, P1115, P1133, P1441 are not present.

•	The fuel trim index is below 70 (-45 percent).

•	Engine coolant temperature is between 60-115°C (140-239°F).

•	The engine speed is between 750-3,200 RPM.

•	The vehicle speed is below 112 km/h (70 mph).

•	The TP angle is below 80 percent.

•	The MAP is above 38 kPa.

•	The above conditions are present for more than 4 seconds.

Action Taken

Malfunction indicator lamp (MIL) illuminates after two consecutive driving cycles with the fault active.

Conditions for Clearing the MIL/DTC

•	The MIL will turn OFF after passing three consecutive diagnostic tests.

•	A history DTC will clear after 40 consecutive ignition cycles have occurred without a fault.

•	History and current DTCs can be cleared by using a scan tool.

Diagnostic Aids

•	Inspect for poor connections at the PCM. Inspect the harness connectors for backed out terminal, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.

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

Test Description

The number below refers to the step number on the diagnostic table.

A clogged air cleaner filter element restricts the airflow coming into the engine. This step checks the condition of the air cleaner filter.

A leaky injector can cause a rich condition and set DTC P0172. Refer to Chart C-2A for further diagnosis.

A loose TP sensor may not set a TP sensor related DTC, but may cause the system to become rich by a higher than actual TP reading.

Step	Action	Values	Yes	No
Schematic Reference: Engine Controls Schematics
1	Was the On-Board Diagnostic (OBD) System Check performed?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	Are any component related DTCs set?	--	Go to component DTC charts	Go to Step 3
3	Ignition ON, engine ON. Operate the vehicle in Closed Loop. Open the scan tool Engine 1 data list. Observe the Fuel Trim Index. Fuel Trim Index should be below specified value. Is the Fuel Trim Index above the specified value?	70	Go to Step 4	Go to Step 5
4	Ignition ON, engine OFF, review the Freeze Frame data and note parameters. Operate the vehicle within the Freeze Frame conditions noted. Using a scan tool, monitor the Fuel Trim Index. Does the Fuel Trim Index go above the specified value while operating under Freeze Frame conditions?	70	Go to Diagnostic Aids	Go to Step 5
5	Visually and physically check the air cleaner filter element for excessive dirt or for being plugged. Replace if needed. Did the air cleaner require replacement?	--	Go to Powertrain On Board Diagnostic (OBD) System Check	Go to Step 6
6	Visually and physically check the air intake system for being collapsed or restricted. Replace if needed. Did the air intake system require repair?	--	Go to Powertrain On Board Diagnostic (OBD) System Check	Go to Step 7
7	Inspect the throttle body inlet for damage or foreign objects which may partially block airflow and correct any problem found. Did the inspection of the throttle body reveal a condition requiring repair or replacement?	--	Go to Powertrain On Board Diagnostic (OBD) System Check	Go to Step 8
8	Ignition OFF and inspect the throttle bore, throttle plate and IAC passages for coking and foreign objects. If a problem was found, repair as necessary. Did the inspection reveal a condition requiring repair?	--	Go to Powertrain On Board Diagnostic (OBD) System Check	Go to Step 9
9	Start the engine with the vehicle in park or neutral and A/C OFF. Note idle quality. Is a low or unsteady idle being experienced?	--	Go to Step 10	Go to Step 12
10	With the engine idling, observe the idle air control (IAC). Is the IAC value below the specified value?	100	Go to Step 12	Go to Step 11
11	Disconnect the MAP sensor electrical connector. Operate the vehicle while in Closed Loop, while monitoring the Fuel Trim Index. Does the Fuel Trim Index increase above specified value?	60	Go to Step 20	Go to Step 12
12	Perform DTC P0506 or P0507 charts to check IAC valve performance. If a problem is found, repair as necessary. Did the inspection reveal a condition requiring repair?	--	Go to Powertrain On Board Diagnostic (OBD) System Check	Go to Step 13
13	Disconnect the vacuum hose from the fuel pressure regulator and inspect the hose for the presence of fuel. If fuel is present in the vacuum hose, replace the fuel pressure regulator. Refer to Fuel Metering System for replacement. Did the fuel pressure regulator require replacement?	--	Go to Powertrain On Board Diagnostic (OBD) System Check	Go to Step 14
14	Ignition ON, engine OFF, monitor the Throt Position display on the scan tool while slowly depressing the accelerator pedal. Does the Throt Position display increase steadily and evenly from its minimum voltage at closed throttle to its maximum voltage at wide-open throttle?	--	Go to Step 15	Go to Step 19
15	Perform the Fuel System Pressure Test, Chart A-7. If the chart isolates a problem, repair as necessary. Did the chart isolate a problem requiring repair?	--	Go to Powertrain On Board Diagnostic (OBD) System Check	Go to Step 16
16	Perform the Evaporative Emissions (EVAP) Control Canister Purge Valve Check. DTC P0441 or P1441 charts. If those DTC charts isolate a problem, repair as necessary. Was a problem isolated that required a repair?	--	Go to Powertrain On Board Diagnostic (OBD) System Check	Go to Step 17
17	Perform the Injector Coil/Balance Test, Chart C-2A. If the chart isolates a problem, repair as necessary. Did the chart isolate a problem requiring repair?	--	Go to Powertrain On Board Diagnostic (OBD) System Check	Go to Step 18
18	Remove and visually/physically inspect the O2S 1 for silicon contamination. This will be indicated by a powdery white deposit on the portion of the sensor exposed to the exhaust stream. If contamination is present on the sensor, find the source of the contamination and repair. Also replace the contaminated O2S. Was contamination present?	--	Go to Powertrain On Board Diagnostic (OBD) System Check	Go to Diagnostic Aids
19	Check the TP sensor mounting screws and tighten or replace them as necessary if they are loose or missing. If the screws are OK, replace the TP sensor. Is the action complete?	--	Go to Powertrain On Board Diagnostic (OBD) System Check	--
20	Replace the MAP sensor. Is the action complete?	--	Go to Powertrain On Board Diagnostic (OBD) System Check	--