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Catalyst Temperature Sensor Circuit High (Bank 1 – Sensor 1)

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Catalyst Temperature Sensor High Input Bank 1 Sensor 1

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– Faulty Catalyst Temperature Sensor
– Catalyst Temperature Sensor harness is open or shorted
– Catalyst Temperature Sensor circuit poor electrical connection

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Main Catalyst Efficiency Below Threshold (Bank 1)

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Main Catalyst Efficiency Below Threshold Bank 1

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– Warm Up Three Way Catalytic converter deterioration or malfunction
– Exhaust system leaks
– Loose front or rear HO2Ss
– Faulty front heater O2 sensor
– O2 sensors harness is open or shorted
– O2 sensors poor electrical connection

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Heated Catalyst Efficiency Below Threshold (Bank 1)

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Heated Catalyst Efficiency Below Threshold Bank 1

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Tech Notes:

– Air leak before catalytic converter
– Faulty oxygen sensor
– Faulty Catalytic Converter

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Technical Definition:

Catalyst System Efficiency Below Threshold (Bank 1)

Technical Description:

The catalytic converter is a part of the exhaust system that looks kind of like a muffler, although it’s job is very different from that of a muffler. A catalytic converter’s job is to reduce emmissions from the exhaust.

Possible Causes:

• Leaded fuel was used where unleaded was called for
• A damaged or failed oxygen sensor (HO2S)
• Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
• The engine coolant temperature sensor is not working properly
• Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
• Retarded spark timing
• The oxygen sensors in front and behind the converter are reporting too similar of readings
• Leaking fuel injector or high fuel pressure
• Cylinder misfire
• Oil contamination

Possible Symptoms:

Catalyst System Efficiency Below Threshold Bank 1

Possible Solutions:

• Check for exhaust leaks at the manifold, pipes, catalytic converter. Repair as required.
• Use a scope to diagnose the oxygen sensor operation (Tip: The oxygen sensor in front of the catalytic converter normally has a fluctuating waveform. The waveform of the sensor behind the converter should be more steady).
• Inspect the downstream heated oxygen sensor (HO2S), replace if necessary
• Replace the catalytic converter
• Overall probably the biggest mistake vehicles owners make when they have a P0420 code is to simply replace an oxygen sensor (H02S). It is important to do proper diagnosis so you’re not wasting money replacing parts unnecessarily.

We strongly recommend that if you need to replace the catalytic converter that you replace it with an OEM unit. Second choice would be a high-quality replacement part. There are many stories in our forums where folks replaced the cat with a cheaper aftermarket one only to have the code return shortly thereafter.

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it’s out of it’s bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It’s worth checking into.

OBD-II Trouble Code Type:

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Tech Notes:

– Three way catalyst converter Bank 1
– Exhaust tube
– Intake air leaks
– Fuel injectors may be faulty
– Fuel injector leaks
– Spark plugs may be faulty
– Improper ignition timing
– Engine Control Module (ECM)

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Technical Definition:

Warm Up Catalyst Efficiency Below Threshold (Bank 1)

Technical Description:

Basically this means that the oxygen sensor downstream of the catalytic converter on bank 1 is detecting that the converter is not working as efficiently as it should be (according to specs). It is part of the vehicle emissions system.

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Warm Up Catalyst Efficiency Below Threshold Bank 1

Possible Solutions:

Measure the voltage at the oxygen sensor on Bank 1 (the rear sensor, or the sensor after the converter). In fact, it would be a good idea to test each oxygen O2 sensor while you’re at it.

One thing to note is that many vehicle manufacturers offer a longer warranty on emissions-related parts. So if you have a newer car but it’s out of it’s bumper-to-bumper warranty, there still may be warranty on this type of problem. Many manufacturers give a five year, unlimited mileage warranty on these items. It’s worth checking into.

OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– Warm Up Three Way Catalytic converter deterioration or malfunction
– Exhaust system leaks
– Loose front or rear HO2Ss
– Faulty front heater O2 sensor
– O2 sensors harness is open or shorted
– O2 sensors poor electrical connection

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Technical Definition:

Secondary Air Injection System Control B Circuit

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Secondary Air Injection System Control A Circuit Malfunction

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Secondary Air Injection System Switching Valve A Circuit Shorted

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Secondary Air Injection System Switching Valve B Circuit

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Secondary Air Injection System Switching Valve B Circuit Open

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Secondary Air Injection System Switching Valve B Circuit Shorted

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Secondary Air Injection System

Technical Description:

The P0410 code refers to the emissions system. The AIR pump puts air to the exhaust to lower emissions. It takes in outside air and pumps it through two one-way check valves into each bank of the exhaust.

Possible Causes:

• Water may have collected in the AIR pump or the vent solenoid and frozen or corroded the pump
• Blown AIR pump fuse due to freezing up

Possible Symptoms:

• MIL illumination obviously
• Hesitation on acceleration
• Noise from a bad/stuck AIR pump

Secondary Air Injection System Malfunction

Possible Solutions:

There is a technical service bulletin (TSB) regarding this code for a number of GM models. The TSB calls for the replacement of the AIR pump and the installation of a new secondary injection hose. The TSB can be found on this ACDelco site.

Additionally, if you simply replace the AIR pump the problem may return again (and again). If you replace the pump, also clean out the hoses and replace the one-way check valve. If this is on a GM model that the TSB applies to, follow those instructions in the link above. In a few cases, people have put a small hole in the rubber cover on the pump which allows any water to drain out.

Also, please note that this may be covered under the emissions warranty on the vehicle. If your vehicle is out of bumper-to-bumper warranty, check if the emissions warranty is still valid!

• Replace the AIR pump AND one-way check valve
• Test and clean the AIR pump AND test and replace the one-way air check valve
• Replace the AIR pump inlet hose
• Replace the AIR pump fuse (found under the hood)

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Tech Notes:

– Faulty Vacuum hoses damaged
– Faulty Air Pump inoperative
– Air bypass solenoid harness is open or shorted
– Air bypass solenoid circuit poor electrical connection
– Air bypass solenoid leaking/blocked or stuck open/closed
– Air diverter valve leaking/blocked or stuck open/closed

Specific Makes:

– Engine hesitation

Technical Definition:

Secondary Air Injection System Incorrect Flow Detected

Technical Description:

Secondary Air Injection is an emission control that uses an air pump (either electric or turned by the drive belt) to move fresh air into the exhaust manifold(s) or exhaust ports when the engine is in open loop and pre-catalytic converter when in closed loop. This reduces hydrocarbon emissions (HC), Carbon Monoxide (CO), and oxides of Nitrogen (NOx). This fresh air helps convert Carbon Monoxide (CO) into Carbon Dioxide (CO2) and Hydrocarbons (HC) into water vapor (H20).

Possible Causes:

• Damaged or missing check valve
• AIR pump intake port plugged/damaged
• AIR pump clutch malfunction
• Holes or damage to exhaust components

Possible Symptoms:

• MIL (Malfunction Indicator Lamp) illumination
• Backfiring in the exhaust under hard acceleration
• Engine running rich (This is counter-intuitive. See explanation below)
• Squealing belt

Secondary Air Injection System Incorrect Flow Detected

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OBD-II Trouble Code Type:

Diagnostic Step:

Tech Notes:

– Faulty Vacuum hoses damaged
– Faulty Air Pump inoperative
– Air bypass solenoid harness is open or shorted
– Air bypass solenoid circuit poor electrical connection
– Air bypass solenoid leaking/blocked or stuck open/closed
– Air diverter valve leaking/blocked or stuck open/closed

Specific Makes:

– Engine hesitation

Technical Definition:

Secondary Air Injection System Switching Valve A Circuit Malfunction

Technical Description:

The Secondary Air Injection System (AIR) Switching Valve is the computer controlled valve that controls the air injection into the exhaust system of the engine (this valve may be integral to the AIR pump). This code deals with a problem on the circuit of the SOLENOID, not the operation of the AIR pump itself.

Possible Causes:

Possible Symptoms:

• MIL (Malfunction indicator lamp) illumination
• Increase in tailpipe emissions
• Engine running rich

Possible Solutions:

• Short to ground on control circuit
• Short to voltage on control circuit
• Control circuit open due to damage, etc.
• Open or short on battery feed circuit to solenoid
• Open or short on battery feed to relay control circuit

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