PZEV Engine
DTC P0171 SYSTEM TOO LEAN (BANK 1)
DTC P0172 SYSTEM TOO RICH (BANK 1)
DTC Detecting Condition:
Wiring Diagram:
CIRCUIT DESCRIPTION
The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim includes the short-term fuel trim and the long-term fuel trim.
The short-term fuel trim is the short-term fuel compensation used to maintain the air-fuel ratio at stoichio- metric air-fuel ratio. The signal from the air-fuel ratio (A/F) sensor indicates whether the air-fuel ratio is RICH or LEAN compared to the stoichiometric air-fuel ratio. This variance triggers a reduction in the fuel volume if the air-fuel ratio is RICH, and an increase in the fuel volume if it is LEAN.
The long-term fuel trim is the overall fuel compensation carried out in long-term to compensate for a continual deviation of the short-term fuel trim from the central value, due to individual engine differences, wear overtime and changes in the operating environment.
If both the short-term fuel trim and the long-term fuel trim are LEAN or RICH beyond a certain value, it is detected as a malfunction and the MIL is illuminated.
HINT:
- When the DTC "P0171" is recorded, the actual air-fuel ratio is on the LEAN side. When DTC "P0172" is recorded, the actual air-fuel ratio is on the RICH side.
- If the vehicle runs out of fuel, the air-fuel ratio is LEAN and DTC "P0171" is recorded. The MIL then comes on.
- If the total of the short-term fuel trim value and long-term fuel trim value is within +35.5 or -30% (engine coolant temperature is more than 80°C), the system is functioning normally.
- The A/F sensor output voltage and the short-term fuel trim value can be read using the hand-held tester or the OBD II scan tool.
- The ECM controls the voltage of terminals AF1A+ and AF1A- of the ECM to a fixed voltage. Therefore it is impossible to confirm the A/F sensor output voltage without the hand-held tester or the OBD II scan tool.
- OBD II scan tool (excluding hand-held tester) displays the one fifth of the A/F sensor output voltage which is displayed on the hand-held tester.
INSPECTION PROCEDURE
HINT:
Hand-held tester only:
Narrowing down the trouble area is possible by performing the "A/F CONTROL" ACTIVE TEST (A/F sensor, heated oxygen sensor or other trouble areas can be distinguished).
a. Perform ACTIVE TEST using the hand-held tester (A/F CONTROL).
HINT: "A/F CONTROL" is an ACTIVE TEST which changes the injection volume -12.5% or +25%.
(1) Connect the hand-held tester to the DLC3 on the vehicle.
(2) Turn the ignition switch ON.
(3) Warm up the engine by running the engine at 2,500 rpm for approximately 90 sec.
(4) Select the item "DIAGNOSIS/ENHANCED OBD II/ACTIVE TEST/ A/F CONTROL".
(5) Perform "A/F CONTROL" with the engine in an idle condition (press the right or left button).
Result:
A/F sensor reacts in accordance with increase and decrease of injection volume:
+25% -> rich output: Less than 3.0 V
-12.5% -> lean output: More than 3.35 V
Heated oxygen sensor 2 reacts in accordance with increase and decrease of injection volume:
+25% -> rich output: More than 0.55 V
-12.5% -> lean output: Less than 0.4 V
NOTICE: There is a few seconds delay in the A/F sensor output and there is about 20 second delay in the heated oxygen sensor 2 output.
The following A/F CONTROL procedure enables to technician to check and graph the voltage outputs of both the A/F Sensor and Heated Oxygen Sensor 2.
For displaying the graph indication, enter "DIAGNOSIS/ENHANCED OBD II/ACTIVE TEST/ A/F CONTROL/USER DATA", then select "AFS B1S1 and O2S B1S2" by pressing "YES" button and push "ENTER" button before pressing "F4" button.
HINT:
- Read freeze frame data using the hand-held tester or the OBD II scan tool. Freeze frame data records the engine conditions when a malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich, etc. at the time of the malfunction.
- A high A/F sensor voltage could be caused by a rich air fuel mixture. Check for conditions that would cause the engine to run rich.
- A low A/F sensor voltage could be caused by a lean air fuel mixture. Check for conditions that would cause the engine to run lean.
Step 1 - 4:
Step 5 - 8:
Step 9:
Step 9 - 10:
Step 11 - 14:
Step 16 - 17:
Step 18 - 19:
Step 20 - 22:
