Buy Saab 900 Oxygen Sensors

A healthy O2 sensor helps fuel economy and cuts emissions. The U.S. Department of Energy notes that fixing a serious problem like a bad oxygen sensor can improve mileage by as much as 40%. (The Department of Energy's Energy.gov)

The Saab 900 was built from 1978-1998 (classic 900 through 1993; "NG" 900 from 1994-1998). U.S. 1996-1998 models use OBD-II. That change added a second sensor after the catalytic converter to watch the converter. Earlier, many cars had only an upstream sensor before the cat. (Wikipedia, NGK Spark Plugs)

• Upstream (Sensor 1): In the exhaust manifold or just after it.
• Downstream (Sensor 2): After the catalytic converter.
  On inline-4 engines, you'll see Bank 1 Sensor 1 (upstream) and Bank 1 Sensor 2 (downstream). On V6 cars, Bank 1 is the side with cylinder #1; you can have sensors on both banks and after the cat(s).

For 1996 U.S. Saab 900 (Trionic OBD-II), Saab added a rear heated O2 sensor after the cat to meet OBD-II rules. (Saab WIS Online)

The O2 (lambda) sensor helps the computer stay near the ideal mix (often explained as 14.7 parts air to 1 part fuel for gasoline) so the catalyst can do its job. (NGK Spark Plugs)

• Check-engine light (MIL)
• Worse MPG
• Rough idle or slow response
• Emissions test failure
  These are typical signs as sensors age, get contaminated, or their heater fails. (Walker Products)

Common generic OBD-II codes tied to Saab 900 O2 sensors include:

• P0135 - O2 sensor heater circuit malfunction (Bank 1, Sensor 1). (OBD-Codes.com)
• P0133 - O2 sensor circuit slow response (Bank 1, Sensor 1). (Edmunds)
• P0141 - O2 sensor heater circuit malfunction (Bank 1, Sensor 2). (OBD-Codes.com)

With a scan tool, a narrow-band upstream O2 will usually switch between ~0.2-0.8 V at warm idle. Little or no switching suggests a problem. You can also watch the catalyst monitor and O2 heater monitor to see if they set "ready" after a drive. State inspection guides explain how the O2, heater, and catalyst monitors work and what "ready" means. (Walker Products, NYVIP3)

Basic steps most owners follow:

1. Let the exhaust cool to safe temp.
2. Disconnect the battery (many makers recommend this).
3. Unplug the sensor, avoid twisting the wire.
4. Remove with an O2-sensor socket.
5. Install the new sensor; use anti-seize only if threads aren't pre-coated, and route the harness away from heat.
6. Torque to spec.
7. Clear codes and road-test.
   NGK's technical guide shows location names (Bank/Sensor), typical 18 mm threads, and installation tips (including anti-seize guidance). (NGK Spark Plugs)

• Many M18 sensors are tightened around 35-45 N·m (26-33 lb-ft) in general install charts. (Ngkntk)
• Saab 900 (1996, 4-cyl turbo) Saab service info lists 55 N·m (41 lb-ft) for the O2 sensor on the affected cars-follow the Saab procedure for your exact engine. (Saab WIS Online)

Unheated 1-2 wire sensors are typically serviced earlier; heated sensors are often checked around 60,000 miles (some last longer). As sensors age, they respond more slowly and fuel economy can drop. (Walker Products)

• Fix exhaust leaks (they skew readings).
• Avoid silicone sealants not marked "sensor-safe"; silicone vapors can poison O2 sensors.
• Use unleaded fuel; lead damages sensors and catalytic converters. (, Process Sensing Technologies, Wikipedia)

Federal law covers most emission-related parts for 2 years/24,000 miles. "Specified major" components (like the catalytic converter and engine computer/OBD device) are covered for 8 years/80,000 miles. Check your state's rules for any added coverage. (US EPA)

• 1978-1993 "classic" 900: Typically one upstream sensor (location varies by engine/exhaust). (NGK Spark Plugs)
• 1994-1995 NG 900: Upstream sensor; some markets added more monitoring.
• 1996-1998 NG 900 (U.S.): Upstream + downstream sensor for OBD-II. (Saab WIS Online)

Drive the car through mixed speeds so monitors can run. State programs explain that catalyst and O2/Heater monitors must complete before inspection. If you recently cleared codes or disconnected the battery, the system needs a drive cycle. (NYVIP3)

If you want to read more, the NGK/NTK Oxygen Sensors guide covers how sensors work, locations, and wiring. Saab's official WIS pages detail 900 O2-sensor changes for OBD-II and torque values. The DOE explains fuel-savings from fixing faults, and EPA explains emissions warranty basics. (NGK Spark Plugs, Saab WIS Online, The Department of Energy's Energy.gov, US EPA)

Q: What does the oxygen (O2) sensor do on my Saab 900?
A: It measures oxygen in the exhaust so the computer can adjust fuel. This keeps power, MPG, and emissions in check. (NGK Spark Plugs)

Q: Where is the upstream vs. downstream sensor?
A: Upstream (Sensor 1) is before the catalytic converter; downstream (Sensor 2) is after the converter.

Q: How many O2 sensors does my Saab 900 have?
A: Earlier cars often used only an upstream sensor. U.S. 1996-1998 cars have upstream and downstream sensors for OBD-II. (, Saab WIS Online)

Q: What's "Bank 1"?
A: Bank 1 is the side of the engine with cylinder #1. Inline-4 cars have only Bank 1. V6 cars have Bank 1 and Bank 2. (NGK Spark Plugs)

Q: What codes point to a bad O2 sensor or heater?
A: Common ones include P0135 (Bank 1 Sensor 1 heater) and P0141 (Bank 1 Sensor 2 heater). You may also see P0133 for slow response. (OBD-Codes.com, Edmunds)

Q: Will a failed O2 sensor hurt my catalytic converter?
A: It can. A sensor stuck "lean" or "rich" can push the mix off target and overheat or stress the cat over time. (Wikipedia)

Q: Can a bad O2 sensor really affect MPG?
A: Yes. DOE says fixing a serious issue like a faulty O2 sensor can improve mileage by up to 40%. (The Department of Energy's Energy.gov)

Q: What's the normal voltage for a narrow-band sensor?
A: When warm at idle, many upstream sensors switch between about 0.2 and 0.8 V. Little to no switching suggests a problem. (Walker Products)

Q: What torque should I use?
A: Follow the service manual. As a Saab example, the 1996 900 (4-cyl turbo) lists 55 N·m (41 lb-ft). Generic M18 charts show about 35-45 N·m for many sensors, but always follow Saab's spec for your exact engine. (Saab WIS Online, Ngkntk)

Q: Do I need anti-seize on the threads?
A: If the new sensor's threads are already coated, don't add more. If not coated, apply a small amount to the threads only-keep it off the tip. (NGK Spark Plugs)

Q: Do I have to replace both sensors at once?
A: Not always, but if one is old and fails, the other may be slow too. Some makers suggest replacing in pairs on the same bank. Diagnose first. (Walker Products)

Q: My check-engine light came on after I cleared codes. Did I install it wrong?
A: After clearing codes or disconnecting the battery, the system needs a drive cycle to set monitors. If a code returns, check wiring, connectors, and live data. (NYVIP3)

Q: What can ruin an O2 sensor?
A: Age/mileage, exhaust leaks, wiring damage, silicone RTV vapors, coolant burning, or leaded fuel. (Walker Products, Process Sensing Technologies, Wikipedia)

Q: Are "air-fuel sensors" different from O2 sensors?
A: Yes. Some cars use wideband air-fuel ratio sensors that read more precisely. Your Saab 900 era mostly uses switching (narrow-band) sensors. Check your engine. (NGK Spark Plugs)

Q: Will replacing the O2 sensor help me pass inspection?
A: If the sensor was the cause, yes-after a proper drive cycle so the O2, heater, and catalyst monitors show "ready." (NYVIP3)

Q: What's covered under the federal emissions warranty?
A: Most emission-related parts (like O2 sensors) are covered 2 years/24,000 miles. Catalytic converters and the engine computer/OBD device are covered 8 years/80,000 miles. (US EPA)

Q: Any Saab-specific install tips?
A: Saab's service info warns don't twist the sensor cable, and on 1996 900 gives a 55 N·m torque. It also notes connector changes on OBD-II cars. (Saab WIS Online)

Q: What tools do I need?
A: O2 sensor socket, ratchet/breaker bar, torque wrench, penetrating oil, safety gloves/eyewear. Warming the bung or using penetrant helps remove stuck sensors. (Walker Products)

Q: What thread size is the sensor?
A: Most switching zirconia sensors use an 18 mm thread (often called M18). (NGK Spark Plugs)

Q: How long do sensors last?
A: Many heated sensors last well past 60,000 miles; unheated ones are serviced sooner. Age, fuel quality, and engine condition matter. (Walker Products)

Helpful reading: NGK/NTK's Oxygen Sensors guide explains sensor types, locations, and install tips; Saab WIS shows 900-specific O2 changes and torque; DOE and EPA cover fuel-saving and emissions warranty basics; state OBD-II programs (like NYVIP) explain readiness monitors. (NGK Spark Plugs, Saab WIS Online, The Department of Energy's Energy.gov, US EPA, NYVIP3)