DTC P0170 & P0173: FUEL TRIM MALFUNCTION
NOTE: On Federal vehicles, DTC P0170 applies to fuel trim malfunction on either bank. On California vehicles, DTC P0170 applies to fuel trim malfunction on bank 1 (cylinders No. 1, 3, and 5). DTC P0173 applies to fuel trim malfunction on bank 2 (cylinders No. 2, 4 and 6).
DTC Set Criteria
Engine is in closed loop control. Intake air temperature is more than 14°F (-10°C). Barometric pressure is more than 11 psi (76 kPa). Volume Airflow (VAF) sensor output frequency is 100 Hz or more. On all vehicles, code will set if long-range fuel correction is less than -12.5 percent, or more than +12.5 percent, for 5 seconds. On Federal vehicles, code will set if short-range fuel correction is less than -12.1 percent, or is more than +12.1 percent on 3.0L engine, or more than +11.7 percent on 3.5L engine, for 5 seconds. On California vehicles, code will set if short-range fuel correction is less than -7.4 percent, or more than +7.4 percent, for 5 seconds.
Engine is in closed loop control. Intake air temperature is more than 14°F (-10°C). Barometric pressure is more than 11 psi (76 kPa). Volume Airflow (VAF) sensor output frequency is less than 100 Hz. On all vehicles, code will set if long-range fuel correction is less than -12.5 percent, or more than +12.5 percent, for 5 seconds. On Federal vehicles, code will set if short-range fuel correction is less than -17.1 percent, or is more than +17.1 percent on 3.0L engine, or more than +16.7 percent on 3.5L engine, for 5 seconds. On California vehicles, code will set if short-range fuel correction is less than -12.4 percent, or more than +12.4 percent, for 5 seconds.
Engine is in closed loop control. Front Heated Oxygen Sensor (HO2S) is active. Code will set if long-range fuel correction is less than -12.5 percent, or more than +12.5 percent, for 5 seconds. Code will also set if short-range fuel correction is less than -30 percent, or is more than +25 percent, for 5 seconds.
Probable Causes
VAF sensor failed.
Fuel injector failed.
Incorrect fuel pressure.
Air intake system leak.
HO2S failed.
Engine Coolant Temperature (ECT) sensor failed.
Intake Air Temperature (IAT) sensor failed.
Barometric Pressure (BARO) sensor failed.
Exhaust system leak.
Incorrect fuel used.
Powertrain Control Module (PCM) failed.
Diagnostic Procedure
NOTE: For terminal identification, see appropriate illustration under TERMINAL IDENTIFICATION in SELF-DIAGNOSTICS - INTRODUCTION article. For circuit and wire color identification, see appropriate wiring diagram in WIRING DIAGRAMS article.
Using scan tool, check data list item No. 13 (intake air temperature). If temperature displayed on scan tool is equal to actual air temperature as measured with a thermometer, go to next step. If temperature displayed on scan tool is not equal to actual air temperature, check intake air temperature sensor circuit. See DTC P0110: INTAKE AIR TEMPERATURE (IAT) SENSOR CIRCUIT MALFUNCTION .
Using scan tool, check data list item No. 21 (engine coolant temperature). If temperature displayed on scan tool is equal to actual engine coolant temperature as measured with a thermometer, go to next step. If temperature displayed on scan tool is not equal to actual coolant temperature, check engine coolant sensor temperature circuit. See DTC P0115: ENGINE COOLANT TEMPERATURE (ECT) SENSOR CIRCUIT MALFUNCTION .
Using scan tool, check data list item No. 25 (barometric pressure). Compare readings with expected values. See BAROMETRIC PRESSURE table. If scan tool reading is as specified, go to next step. If scan tool reading is not as specified, check barometric pressure sensor circuit. See DTC P0105: BAROMETRIC (BARO) PRESSURE SENSOR CIRCUIT MALFUNCTION .
BAROMETRIC PRESSURE
Altitude - Ft. (m) kPa
0 (0) 101
1969 (600) 95
3937 (1200) 88
5906 (1800) 81
Disconnect fuel injector connectors. (All fuel injectors on Federal vehicle, fuel injectors No. 1, 3 and 5 on California vehicle with DTC P0170, or fuel injectors No. 2, 4 and 6 on California vehicle with DTC P0173.) Check resistance between fuel injector terminals. Resistance should be 13-16 ohms at 68°F (20°C). If resistance is as specified, go to next step. If resistance is not as specified, replace fuel injector, then go to step 13 .
Check wiring between injectors and PCM 35-pin connector C-89. Also check fuel injector connectors, intermediate connector and PCM connector C-89. If problem exists, repair as necessary, then go to step 13 . If problem does not exist, go to next step.
Perform fuel pressure test. See FUEL PRESSURE under FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. If fuel pressure is within specification, go to next step. If fuel pressure is not within specification, repair as necessary, then go to step 13 .
Using scan tool, check data list item No. 81 (long-term fuel trim). If fuel trim is more than zero (during closed loop), go to next step. If fuel trim is less than zero (during closed loop), go to step 11 .
Check for restrictions to airflow or for air or vacuum leaks in intake system. If problem exists, repair as necessary, then go to step 13 . If problem does not exist, go to next step.
Using scan tool, check data list item No. 12 (volume airflow). On 3.0L engine, reading should be 25-51 Hz at idle and 74-114 Hz at 2500 RPM. On 3.5L engine, reading should be 18-44 Hz at idle and 58-98 Hz at 2500 RPM. If scan tool reading is not as specified, replace VAF sensor, then go to step 13 . If scan tool reading is as specified, go to next step.
Check for fuel filter and/or fuel line blockage. Check for clogged injectors. Check fuel pump output volume. Check fuel for contamination. Check for exhaust leaks. If problem exists, repair as necessary, then go to step 13 . If problem does not exist, replace PCM, then go to step 13 .
Using scan tool, check data list item No. 12 (volume airflow). On 3.0L engine, reading should be 25-51 Hz at idle and 74-114 Hz at 2500 RPM. On 3.5L engine, reading should be 18-44 at idle and 58-98 at 2500 RPM. If reading is within specification, go to next step. If reading is not within specification, replace VAF sensor, then go to step 13 .
Check for fuel injector leakage. Check fuel for contamination. If problem exists, repair as necessary, then go to next step. If problem does not exist, replace PCM, then go to next step.
Using scan tool, clear DTCs. Test drive vehicle following OBD-II drive cycle fuel trim monitor pattern. See OBD-II DRIVE CYCLES under VERIFYING REPAIRS in SELF-DIAGNOSTICS - INTRODUCTION article. Check for DTCs. Confirm DTC does not reset. See VERIFYING REPAIRS in SELF-DIAGNOSTICS - INTRODUCTION article.
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