Question about 1997 Volkswagen Jetta

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I went for an emissions test today and it failed the mechanic said the car might be running too hot or too lean also notice the the heat gauge stays at cold when driving.HELP

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  • David Melrose May 11, 2010

    what did you fail for? High Nox or somthing else?

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I suspect you need a new thermostat. It should be running at 195 degrees F.

If the engine does not fully warm up, the engine can not go into emission control mode.

The engine temperature sensor sends a signal to the engine/emissions computer that the engine is now at normal operating temp. The computer then starts controlling fuel flow, EGR, etc. so that emissions are being controlled.

When the enigne is cold, you are in what we call "open loop" meaning no emission control.

Get the thermostat installed first. Make sure it's the same temp rating as the one that's in there. Either 180 degrees or 195 degrees.

Then you should pass.

Posted on Mar 03, 2009

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I have a 89 buick electra 98000 miles I failed emissions for high co at idle I put a obd1 tester on it it showed vehicle was not going into closed loop I replaced oxygen sensor it then went into closed...


to stay in close loop o2 sensor have to be hot
and the converter catalyst is the one who keep the heat......
converter is it factory or never been change.
with scanner obd1 you should see the voltage variation of o2 sensor. it should go from lean to rich . .500mv is the middle then under .500mv is lean and over it is rich.......with this information ecm correct the fuel delivery
hope it helps

Sep 29, 2013 | 1989 Buick Electra

1 Answer

Wont start for 10 min


Have your charging system tested and include the Battery. Go to Autozone.com ,register your vehicle for free, get free wiring diagrams and Fusebox layouts. Have a starter draw test done.

Check the relays for the fuelpump, ignition, and PCM. Sometimes the horn relay can be the same part number and be interchanged.

What you are describing can be many things. You have more compression in a hot engine, you have different timing in a hot engine because vehicles run so lean today. The O2 sensors may be keeping the engine too lean to restart after a warmup. Relays can overload when hot and kick out the connections. Your fuelpump can be failing.

You did not indicate how far you drive when this happens. If you are driving 10 miles a weak battery will not recharge, but a 100 mile trip gives it more opportunity. The starter draw test will tell if the starter is bad. The starter may cool down overnight, but frequent restarts may heat the starter with it failing.

Jul 24, 2012 | 2007 Chevrolet Colorado (Extended Cab) New...

1 Answer

Hard time starting when warm/hot.


This can be due to the Lean condition of the fuel ratio. The heat sensors need to cool down to put the engine into a "cold start routine". If the heat sensors are not cooling, then it will be hard to start.

Poor grade of fuel. Each grade of fuel has an ignition point. With the engine in Lean mode, the flash ratio prevents easy starting. You could also have a bleed down of fuel or a malfunction in the Evaporative emission system. This is now requiring your car to repressurize the system due to a bad solenoid or a faulty emissions line.

I hope my solution is helpful..

Jun 08, 2012 | Honda Cars & Trucks

1 Answer

2004 Jeep Grand Cherokee temp gauge high when heat is on


If your "check engine" light is turn on, I suggest scanned the PCM to know exactly what fault code is stored there. Additionally, could be some problem with the "temp sending unit".

Keep us updated.

Jan 23, 2012 | 2004 Jeep Grand Cherokee

1 Answer

I have an 04 cavalier. Code P0172 mechanic changed upstream 02 senor. light came back on. Brought back to mechanic he changed the downstream, light came back on. I changed fuel filter, spark plugs, oil...


Think your guy changed O2 Sensors ,
but didn't consider that your sensors PO172
is rich,because it is correcting for a lean condition


I'am going to really guess here

The EVAP has leaks,but no codes set,
partially driving the system lean (Vacuum Leaks)

The Converter is sort of out there as
not working well either

I would smoke the EVAP System and everything else,
intake manifold etc

I think you will find this by MAYBE even just looking
for a bad hose leak

Is that data from your mechanics scanner ?
What is their theory ?

Bank 1 has a vacuum leak I think !! ??

Mar 19, 2011 | Chevrolet Cavalier Cars & Trucks

1 Answer

I failed the NOX portion of the emissions test app.standard is 4.00 i ran a 6.32 . I had a cat conv. put on two years ago. I just noticed my temp. gauge not moving at all could this be the problem? Do you...


Engine not at operating temperature--Cold Converter,Thermostat Stuck Open
Malfunctioning Mixture Control--O2 Sensor reading lean all the time.
Coolant Temp Sensor high resistance or open circuit
Bad Converter

EGR Valve--most likely cause

Nov 11, 2010 | 1993 Isuzu Trooper

2 Answers

Engine running to lean


I had the same problem...Just went into mechanics today, EGR system was shot.

May 05, 2009 | 1995 Eagle Talon

1 Answer

Price to fix Emissions


BEFORE YOU CAN ESTIMATE THE COST YOU WILL HAVE TO FIND OUT WHY THE TRUCK IS RUNNING LEAN, IT COULD BE FUEL PRESSURE, AN INTAKE MANIFOLD VACUUM LEAK AND SO ON, THEY WILL MOST LIKELY THEY WILL QUOTE YOU 2 HOURS LABOR TO START AND DIAGNOSTICS, OR ABOUT $200

Dec 01, 2008 | 2001 Ford Explorer Sport Trac

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