General Precautions of EFI System Maintenance
F-26
28. P0131 Upstream Oxygen Sensor Signal Circuit Voltage Too Low (Malfunction of
Circuit Short to Ground)
Description about Malfunction Cause:
After engine has been started, ECU examines voltage of upstream oxygen sensor circuit. If signal voltage is
less than 0.06V longtime, it is determined to be the malfunction of upstream oxygen sensor signal circuit short
to ground.
Malfunction Diagnostic Guide:
Required Equipment: (Diagnostic Instrument with EOBD Diagnostic Function, Digital Multimeter, and
Correct Circuit Diagram)
Step I: Use diagnostic instrument to read the malfunction information
Read Result I Read Result II
MIL Lamp On P-CODE Present MIL Lamp Off P-CODE Present
P0131
P0131
Maintenance tips:
The malfunction has been confirmed, and the
following problems may possibly exist
1) The circuit connected to Pin 18# of ECU and
36# of ECU in short circuit.
2) The circuit connected to Pin 18# of ECU short
to ground
Maintenance tips:
The malfunction is not ultimately confirmed and it
may possibly be a random malfunction. Inspect the
following items:
1) Measure resistance between ECU Pin 18# and
36#
2) Measure voltage on ECU Pin 18#
29. P0132 Upstream Oxygen Sensor Signal Circuit Voltage too High (Circuit
Shorted to Power Supply)
Description about Malfunction Cause:
After engine has been started, ECU performs measurement on the circuit voltage of upstream oxygen sensor,
and will determine it to be the signal circuit of upstream oxygen sensor short to power supply, when signal
voltage is higher than 1.5V for a long time.
Schematic Circuit:
Main relay
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