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Discussion Starter #1
I have a 1996 Saab 9000 CS and every now and then my check engine light comes on. Usually when I am stuck in traffic. The code is P0133 which is says is Oxygen Sensor Bank 1 Sensor 1 slow response time.
If I have found the right info the sensor should be reading somewhere above and below .4 volts. I logged data for the O2 sensor voltage and for the most part it seems good. It goes up and down between .2 and .8 for quite a while but then it has about a 10 second stretch where it just says 0 and then it works fine again and then it has another 25 second stretch where it says 0 and then goes back to normal. Does that just mean the O2 sensor is bad or is there something else that could cause this problem?
Also, it may or may not be related but my car has been pretty slow to get up to temperature. And once it does get up to temperature sometimes it will go back down to just above the L. And eventually it will go back up to normal. Could that be just a faulty thermostat or is something else happening?
If anyone is interested here is a link to the data I logged.!435&authkey=!AGvDGLddQYQPa3s
The 0 reading shows up at 2:31:39
Thanks for any help!

2,026 Posts
There is a lot of rhetoric and requires access to an ISAT, but basically, they offer 2 possible causes and 2 solutions:


1. Insulation faults (in the associated wiring or within the sensor itself)

2. A failed probe


1. Repair the wiring

2. Replace the sensor

I like the moisture theory best (italics, bold, 3 font)


Symptom Of Fault .
The CHECK ENGINE lamp (MIL) is on. Any other diagnostic trouble codes (such as misfiring, closed loop, adaptation).

Conditions .
P0130: All-embracing DTC.
P0132: Ignition switch in ON position.
Sensor voltage > 1500 mV for more than 5 sec.
P0133: Diagnosis not yet performed this trip.
Speed = 0.
Idling speed.
Closed loop active.
Coolant temperature > 60°C (> 140°F) .
Oxygen sensor heating current < 1500 mA .
Oxygen sensor voltage oscillates at too low a frequency.

Diagnostic Help .
Operation of the oxygen sensor can be ascertained using an ISAT scan tool.

  • Select "READ FUNCTIONS".
  • Select "O2S 1".
When closed loop is active the ISAT scan tool reading should oscillate between 0.1 and 0.9 V .

If the reference ground or sensor voltage of any of the oxygen sensors is short-circuited to battery positive (B+) in the wiring harness or in any of the oxygen sensors, DTCs P0132 and P0138 will probably both be generated.
The control module inputs of the oxygen sensors are high-ohmic. If moisture gets into the connectors of some of the oxygen sensors, a diagnostic trouble code will be generated.

Diagnostic Procedure .

  1. Check additional diagnostic trouble codes in the Trionic system
    • Obtain readouts of all diagnostic trouble codes using the ISAT scan tool.
Are P0132 and P0138 present?

  • Continue with point 2.

  • Continue with point 3.
  1. One of the oxygen sensor leads connected to electronic control module pin 23, 70 or 47 is short circuited to battery positive (B+) in the wiring harness or in one of the oxygen sensors.
Check the insulation of the oxygen sensors.

  • Unplug the 4-pin connectors of both oxygen sensors.
  • Check the resistance of both sensors
  • pins 1-3: OL (OverLoad = infinite resistance)
  • pins 1-4: OL (OverLoad = infinite resistance)
Are all readings OK?

  • Rectify the lead between the connectors of both sensors and pin 23, 70 or 47 of the electronic control module and then proceed to point 4.

  • Change the relevant oxygen sensor and proceed to point 4.

  1. Check the oxygen sensor's electrical interfaces
    • Unplug the oxygen sensor's 4-pin connector.
    • Replace the sensor with a conventional 1.5 V battery in good condition.
    • Connect the battery's positive (+) pole to pin 4 of the connector.
    • Connect the battery's positive(+) pole to pin 3 of the connector.
    • Ignition switch in ON position.
    • Connect an ISAT scan tool.
    • Select "READ FUNCTIONS".
    • Select "O2S 1".
Does the ISAT scan tool show about "1.4"V?

  • Change the oxygen sensor and continue with point 4.

  • Check the leads between:
pin 4 of the connector and pin 23 of the control module and between pin 3 of the connector and pin 47 of the control module for continuity or shorting and repair or replace them as necessary.
Then continue with point 4.

  1. Final check:
    • Clear the diagnostic trouble code.
    • Implementation of driving cycle:
    • Ignition switch in the ON position, A/C switched off and temperature sensor unplugged from the EDU so that the radiator fan runs continuously.
    • Start the engine and run it at idling speed until the temperature of the coolant exceeds 60°C (140°F) or for at least 1 minute if this temperature is reached earlier.
    • Depress the accelerator for a second or so and then let the engine run at idling speed for 30 seconds. Do this twice again.
    • Evaluation of driving cycle:
    • Connect an ISAT scan tool.
    • Select "ON/OFF".
    • Select "O2S 1 ".
Does the ISAT scan tool show "NOT READY"?

  • Repeat the driving cycle.

  • Check whether the diagnostic trouble code has recurred.
Has the diagnostic trouble code recurred?

  • Proceed at "Before Replacing a Control Module". See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Component Tests and General Diagnostics

  • The remedial measure taken was correct.
  • Plug the temperature sensor into the EDU.
  • Clear the diagnostic trouble code for the temperature sensor in the EDU.

3,938 Posts
O2 sensors are very reliable (no moving parts!) and very durable. Many are replaced for no reason at all.

Thermostat failure used to be so common I just replaced mine routinely every couple of years when the coolant was flushed.

However, I must say the later thermostats seem much more reliable.

If your thermostat is five years old replace it, especially if the coolant should be flushed (every two years regardless of mileage is best practice). Brake fluid should also be flushed every two to three years regardless of mileage. I often specify both services at the same time, every second oil change.
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