2002 Volkswagen Golf

NICOLE81620

MEMBER
2002 VOLKSWAGEN GOLF
4 CYL
FWD
AUTOMATIC
94,000 MILES

My check engine light is on and I had the codes scanned. It came back with 2- the first one was P1296- Cooling System Malfunction and second P0420- Catalyst system efficiency below threshold bank 1. I checked my coolant level and it is not low and I have had no problems driving the car. It has a brand new water pump and timing belt and the temperature gauge on my dashboard never exceeds 190 degrees so I do not think there is anything wrong with the cooling system itself. I have noticed a strong gas smell from the exhaust when I start it. Is it possible the two things are related at all? Or is it more likely that I just have two blown sensors. Or neither? Thanks!

1 Reply

MATHIASO

MECHANIC
1,209 POSTS

Hello nicole81620

The two codes point at two different systems but there one thing in common

Trouble Code: P1296

Cooling System Malfunction
Possible Causes:

Engine coolant temperature sensor has failed

An open circuit or a short to B+ is present

Sensor circuit is short to ground

ECM has failed

Trouble Code: P0420

Catalyst System Efficiency (Bank 1) Below Threshold
Possible Causes:

Air leaks at the exhaust manifold or in the exhaust pipes

Catalytic converter is damaged, contaminated or it has failed

ECT/CHT sensor has lost its calibration (the signal is incorrect)

Engine cylinders misfiring, or the ignition timing is over retarded

Engine oil is contaminated

Front HO2S or rear HO2S is contaminated with fuel or moisture

Front HO2S and/or the rear HO2S is loose in the mounting hole

Front HO2S much older than the rear HO2S (HO2S-11 is lazy)

Fuel system pressure is too high (check the pressure regulator)

Rear HO2S wires improperly connected or the HO2S has failed

Note: When looking carefully at the two codes, there is one thing in common and that is the coolant sensor. Computer rely on the coolant sensor to adjust fuel mixture. When computer add to much fuel when it should not because of a lazy coolant sensor, it could lead to catalytic converter and oxygen sensor damage.A damage or fouled oxygen sensor will probably give wrong information to the computer too.
What you need to do is to check the wiring to the coolant sensor for open or short. If there is no wiring problem, test or replace the coolant sensor.
Next, have the catalytic converter replaced along with the oxygen sensor.