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Code 78 APPS Main and Code 79 TPS Main are diagnostic trouble codes (DTCs) that can appear on a 1997 Mitsubishi Pajero.
Code 78 APPS Main: This code indicates that the APPS (Air Pump System) Main relay is not working properly. The APPS relay is responsible for supplying power to the air pump, which is used to control the air-fuel mixture.
Code 79 TPS Main: This code indicates that the TPS (Throttle Position Sensor) Main circuit is not working properly. The TPS sensor is responsible for sending information to the engine control unit (ECU) about the position of the throttle valve.
If either of these codes appears, it is important to have the vehicle diagnosed by a qualified mechanic to determine the cause of the problem. The mechanic may need to test the APPS relay, the TPS sensor, or other components in the fuel system.
Here are some possible causes of Code 78 APPS Main and Code 79 TPS Main:
Faulty APPS relay: The APPS relay may be faulty and not be supplying power to the air pump properly.
Faulty TPS sensor: The TPS sensor may be faulty and not be sending accurate information to the ECU about the position of the throttle valve.
Clogged air filter: A clogged air filter can restrict airflow to the engine and cause the APPS relay to overheat and malfunction.
Low fuel pressure: Low fuel pressure can cause the APPS relay to overheat and malfunction.
Faulty wiring: The wiring to the APPS relay or TPS sensor may be damaged or corroded, causing the codes to appear.
If you are experiencing problems with your 1997 Mitsubishi Pajero and either Code 78 APPS Main or Code 79 TPS Main appears, it is important to have the vehicle diagnosed by a qualified mechanic to determine the cause of the problem and to get it repaired as soon as possible.
Sounds like you have a cracked heat exchanger, and combustion gases are getting into the circulation air. GET IT CHECKED AND CORRECTED IMMEDIATELY. Combustion gases contain carbon monoxide, you may be getting carbon monoxide into your home. Do you have a carbon monoxide detector?
Catalyst System efficiency below threshold means that the O2 sensor behind the catalytic converter is reading more hydro carbons than what it views as normal. Either, your catalytic converter is bad and not changing the carbon monoxide into less volatile gases or you have something upstream causing the issue; it is running too rich, etc.
Upstream sensors ( before the catalytic converter ) are responsible for initial fuel air mix, and Down stream sensors are responsible for Carbon Monoxide levels as well as other emissions.
high hydrocarbons indicates head gasket(1 or both) leaking , carbon monoxide is a worn out catylitic convertor which both could lead to the oxy sensor getting a false reading
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