* Bank 1: In a V6 engine (like the Astro's), Bank 1 refers to the side of the engine that contains cylinder #1. Your engine's layout will determine the exact physical location, but it's generally the driver's side (in the US).
* Sensor 3: This is the *post-catalytic converter* oxygen sensor on Bank 1. There's usually a sensor before the catalytic converter (Sensor 1) and one after (Sensor 3). The pre-cat sensor monitors the exhaust *before* the catalytic converter, while the post-cat sensor (Sensor 3) monitors its effectiveness.
* Low Voltage/Heater Circuit: Oxygen sensors have internal heaters to ensure they reach operating temperature quickly. "Low voltage" indicates a problem with the sensor's heater circuit—either a faulty sensor, wiring issue (broken, corroded, or short), or a problem with the electrical connection.
* Cylinder Misfire: This is a separate issue, but often related. A misfire (one or more cylinders not firing properly) can contaminate the exhaust, causing inaccurate readings from the post-cat O2 sensor (Sensor 3) and potentially triggering the low-voltage code. A faulty O2 sensor *could* also indirectly contribute to a misfire, though less likely in this scenario.
Where to find it:
You'll need to consult a repair manual specific to your 1999 Chevy Astro AWD. However, generally:
1. Locate Bank 1: As mentioned, this is usually the driver's side.
2. Locate Catalytic Converter: It's a metal canister in the exhaust system.
3. Sensor 3 (Post-Cat O2 Sensor): This sensor will be located downstream (after) the catalytic converter on Bank 1's exhaust pipe. It will be a threaded sensor with a wire harness connected.
Troubleshooting:
1. Visual Inspection: Check the wiring harness to Sensor 3 for any obvious damage, corrosion, or loose connections.
2. Check the sensor itself: Look for physical damage to the sensor.
3. Advanced Diagnostics: Use an OBD-II scanner to get more specific information about the misfire (which cylinder(s) are affected). This will help you identify whether a faulty spark plug, ignition coil, fuel injector, or other component is to blame.
4. Professional Help: If you're not comfortable diagnosing and repairing this yourself, take your Astro to a qualified mechanic. They have the tools and expertise to properly diagnose and fix the problem.
Ignoring this issue could lead to further engine damage, decreased fuel economy, and emission system problems. Addressing both the oxygen sensor issue and the misfire is important for proper engine function.
