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Home >> Toyota >> 2001 >> Sienna CE >> Repair and Diagnosis >> External Pages >> Different car >> Section 96 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0171, DTC P0172, DTC P0174 & DTC P0175 >> Diagnostic Aids

Diagnostic Aids

WARNING: This page is about a different car, the 2003 Lexus ES 300. However, it is still accessible from the selected car via links, so may be relevant.
  1. When DTCs P0171 or P0174 are recorded, actual air-fuel ratio is lean. When DTCs P0172 or P0175 are recorded, it is rich.
  2. If vehicle runs out of fuel, air-fuel ratio is lean and DTCs P0171 or P0174 are recorded. MIL then illuminates.
  3. Short-term and long-term fuel trim value should be within plus or minus 35 percent of each other at 167°F (75°C).
  4. Air/fuel ratio sensors (bank 1, 2 sensor 1) output voltage and short-term fuel trim value can be read using OBD-II scan tool or hand-held tester.
  5. ECM controls voltage of AFR+, AFL+, AFR- and AFL- terminals at ECM to a fixed voltage. It is impossible to confirm A/F sensor output voltage without using a scan tool. A/F sensor output voltage on OBD-II scan tool is displayed at one fifth voltage of that displayed on hand-held tester. See Figure.
  6. Using a hand-held tester, it is possible to narrow down trouble area by performing ACTIVE TEST of "A/F CONTROL" (oxygen sensor or another can be distinguished).
  7. Connect hand-held tester to DLC3. See Figure.
  8. Turn ignition switch on.
  9. Warm up engine with engine speed at 2500 RPM for approximately 90 seconds.
  10. Perform "A/F CONTROL" at idle condition (press right or left button). Air/fuel ratio sensor and oxygen sensor react simultaneously with increase and decrease of injection volume (+25 percent to rich output: one volt, -12.5 percent to lean output: zero volts). There is a few second delay in sensor 1 (front air/fuel ratio sensor) output. There is about 20 seconds delay in sensor 2 (rear oxygen sensor). See Figure.
  11. To display a graph indication, select and push the "YES or NO" button 2 data "AFS B1S1 and O2S B1S2" or "AFS B2S1 and O2S B2S2" and press button "4" after selecting "ACTIVE TEST/AF CONTROL/USER DATA".
  12. Read freeze frame data using hand-held tester or OBD-II scan tool, as freeze frame data records engine conditions when a malfunction is detected. When troubleshooting, it is useful to determine whether vehicle was running or stopped, engine was warmed up or not, air-fuel ratio was lean or rich, etc. at time of malfunction.
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