Diagnostic Chart
DTC P0125 INSUFFICIENT COOLANT TEMPERATURE FOR CLOSED LOOP FUEL CONTROLCIRCUIT DESCRIPTION
DTC Detecting Condition:
To obtain a high purification rate for the CO, HC and NOx components of the exhaust gas, a three-way catalytic converter is used, but for the most efficient use of the three-way catalytic converter, the air-fuel ratio must be precisely controlled so that it is always close to the stoichiometric air-fuel ratio.
The oxygen sensor has the characteristic whereby its output voltage changes suddenly in the vicinity of the stoichiometric air-fuel ratio. This is used to detect the oxygen concentration in the exhaust gas and provide feedback to the computer for control of the air-fuel ratio.
When the air-fuel ratio becomes LEAN, the oxygen concentration in the exhaust increases and the oxygen sensor informs the ECM of the LEAN condition (small electromotive force: < 0.45 V).
When the air-fuel ratio is RICHER than the stoichiometric air-fuel ratio the oxygen concentration in the exhaust gas is reduced and the oxygen sensor informs the ECM of the RICH condition (large electromotive force: > 0.45 V). The ECM judges by the electromotive force from the oxygen sensor whether the air-fuel ratio is RICH or LEAN and controls the injection time accordingly. However, if malfunction of the oxygen sensor causes output of abnormal electromotive force, the ECM is unable to perform accurate air-fuel ratio control.
The main heated oxygen sensors include a heater which heats the zirconia element. The heater is controlled by the ECM. When the intake air volume is low (the temperature of the exhaust gas is low) current flows to the heater to heat the sensor for accurate oxygen concentration detection.
HINT:
- After confirming DTC P0125, use the OBD II scan tool or hand-held tester to confirm voltage output of the A/F sensor (bank 1, 2 sensor 1) from the CURRENT DATA
- The ECM controls the voltage of the AFR+, AFL+, AFR- and AFL- terminals of the ECM to the fixed voltage. Therefore, it is impossible to confirm the A/F sensor output voltage without the OBD II scan tool or hand-held tester.
- 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.
CONFIRMATION DRIVING PATTERN
Confirmation Driving Pattern:
a. Switch the hand-held tester from the normal mode to the check mode. *1
b. Start the engine and let the engine idle for 100 seconds or more. *2
c. Drive the vehicle at 40 km/h (24 mph) or more for 20 seconds or more. *3
d. Let the engine idle for 20 seconds or more. *4
e. Repeat the procedure *3 and *4 three times.
f. Let the engine idle for 30 seconds. *5
g. Check the O2 sensor output voltage.
HINT: If a malfunction exists, the check engine warning light comes on.
NOTE: If the conditions on this test are not strictly followed, the malfunction will not be detected.
Wiring Diagram:
Step 1 - 3:
Step 4 - 9:
Step 10 - 12:
INSPECTION PROCEDURE
HINT: Read freeze frame data using hand-held tester or OBD II scan tool. Because freeze frame records the engine conditions when the 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.
CHECK FOR INTERMITTENT PROBLEMS
Hand-held tester only:
By putting the vehicle's ECM in the check mode, 1 trip detection logic is possible instead of 2 trip detection logic and sensitivity to detect open circuits is increased. This makes it easier to detect intermittent problems.
1. Clear the DTC.
2. Set the check mode.
3. Perform a simulation test.
4. Check the connector and terminal.
5. Handle the connector.