18
Heated oxygen sensors diagnostic
An S80 car with EMS system that meets ULEV2/EU-
RO4 legal demands is fitted with two heated oxygen
sensors per bank. The upper sensor is fitted before the
CCC and the second sensor after the CCC and before
the UFC (under floor catalyst). The upper sensor is
linear type and the second is a binary type.
The upper sensors have the following monitoring:
- Slow activation (P-code P0134 and P0154). When
the Oxygen sensor heater circuit start to heat up the
element, a delay counter is activated. After a specified
time of heating is a judgment done by evaluating sen-
sor element impedance. Continues monitoring.
- Slow response (P-code P0133 and P0153). A dither is
added to target lambda. The diagnose will then check
if the lambda value can follow this square wave. When
the sensor is slow enough to give high emission it will
be detected as malfunctioning. Performed once per
driving cycle.
- Heater circuit (P-code P0031, P0032 and P0051,
P0052). The sensor heater is continuously monito-
red. Fault will be detected if circuit is: Open, short to
ground or short to battery.
- Sensor circuit (P-code P0131, P0132 and P0151 and
P0152). The sensor circuit is continuously monitored.
Fault will be detected if sensor circuit is: Open, short
to ground or short to battery.
- The second sensors have the following monitoring:
- Sensor circuit (P-code P0137, P0138 and P0157,
P0158). The sensor working range is checked to detect
if sensor have an amplitude/range problem to work in
its normal voltage range. Sensor must be able to work
in catalyst monitoring area to be judged as normal and
be close to 0V after fuel cut. Function also monitor if
sensor is stuck in range.
- Heater circuit (P-code P0037, P0038 and P0057,
P0058). The sensor heater is continuously monito-
red. Fault will be detected if circuit is: Open, short to
ground or short to battery.
- Sensor out of range (P-code P1137, P1138 and
P1157, P1158). If sensor doesn’t work in its normal
range, fault will be detected. Continuous monitoring.
Enable condition
Minimum
Maximum
UHEGO heater On operation Duty Low Level
7.7 ms
UHEGO heater On operation Duty High
120ms
After start delay
30s
Typical Heated Oxygen Sensor diagnostic enable conditions
Malfunction criteria
Threshold value
O2 Sensor Heater fault flag.
5.12s
Element impedance too high
>
80 Ω during 10 s
Typical Heated Oxygen Sensor malfunction thresholds
