Oxygen sensor 2000 galant

code p 0171 refers to system too lean bank 1===causes ---intake /exhaust leak---AIR system---MAF/VAF sensor/s---fuel pressure/ pump---injector/s---heated oxygen sensor (HO2S) the one in the exhaust manifold for bank 1 nearest the firewall

A v-6 or v-8 engine will have two banks. Bank one is the side of the engine with the number 1 cylinder. Bank 2 is the other side of the engine. In your case Bank 1 is cylinders 1-3-5 on the back side of the engine closest to the firewall. Bank 2 is cylinders 2-4-6 on the other side of the engine.

You have two cats bank 1 and bank 2. There are two oxygen sensors before each cat that help determine fuel trim and are refered to as sensor 1 and two oxygen sensors after the cats that monitor cat efficiency and are referred to as sensor 2. The bank 1 sensor 2 O2 sensor is either providing a higher than expected signal or is switching like the sensor 1 O2's. If either of these has occurred the PCM detects that the cat is no longer working as it should and sets the code/turns on the check engine light.

9 times out of 10 it is a cat that has gone bad.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

Bank one sensor is going to be in the front of your catalytic converter and bank two will be to the rear of it. This way your ECM knows how well the cat is working. It will read the oxygen content before the cat and then after.

16716/P0332 - Knock Sensor 2 (G66): Signal Too Low Possible Symptoms

• Irregular rpm
• Drivability problems
• Loss of power
• Engine damage

Possible Causes

• Circuit G66 short to Ground
• Circuit G66 open
• G66 improperly torqued
• G66 damaged
• Control Module damaged

16804/P0420/001056 - Catalyst System; Bank 1: Efficiency Below Threshold Possible Causes

• Leakage in Intake and/or Exhaust System
• Catalyst faulty
• Oxygen Sensor(s) faulty
• Oxygen Sensor(s) Control faulty

Possible Solutions

• Check Intake and Exhaust System for Leaks
• Check Catalyst
• Check Oxygen Sensor(s)
• Check Oxygen Sensor(s) Control
  • Perform Oxygen Sensor(s) Aging Check

have the engine light code scanned, and it'll tell you if it's bank 1 sensor 1, bank 1 sensor 2, bank 2 sensor 1, bank 2 sensor 4.

Bank 1 is on the same side as Cylinder 1
Bank 2 is on the opposite side of Cylinder 1

Sensor 1 is located before the catalytic converter.
Sensor 2 is located after the catalytic converter

P0157 Oxygen Sensor Circuit Low Voltage (Bank 2 Sensor 2)

I would try replacing the Oxygen sensor, then clear the code.

The O2 sensor would be the after the catalytic converter ( sensor 2) on the exhaust pipe of the number 2 cylinder uses ( bank 2).

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I looked up the codes you posted.
P0420 is showing a bad oxygen sensor on bank #1, the one down by the catalytic converter.
P0773 is an electrical problem with the shift solenoid E.
A bad oxygen sensor would cause lower fuel milage.

If you have changed out the parts and still get the codes you probably need to have the ECM reset. The dealer can do that for you or a repair shop that has the scan tool.

The first sensor closest to the exhaust manifold is for the air to fuel ratio. The second one if it has one will be further downstream and checks to see if exhaust is plugged.

Is your car running right especially at idle????