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8

You didn't mention which engine is in your Jetta, but the Mk IV VWs, especially the VR6 engine, are known to have brittle ignition coil housings that crack and admit water, which leads to misfires. After the engine has run for a while, it burns off this moisture and it starts running fine again. Some VWs were subject to a recall to fix this issue. Based on ...


6

The CEL trigger implementation will vary across vehicles, but here are a few for you to try out. They should not have any negative effect in the long-term on the vehicle: P010x - unplug MAF sensor P030x - unplug a spark plug wire/coil (unplugging the corresponding injector is recommended) P0420/P0430 - unplug the O2 sensor after the catalytic converter


6

@JPhi1618 answer is good. I would just add a few more, You can unplug the EGR Valve electrical connector, no harm to engine. Pull out a coil pack or coil wire.


6

Start unplugging stuff. The engine will normally run with a lot of the sensors unplugged, but the check engine light will come on quickly. Some easy to reach ones: Mass Air Flow (MAF), Oxygen sensors, sometimes the throttle position indicator (on the throttle body). If you can unplug the power to the secondary air injection pump, it will cause a fun ...


6

It is most likely that this sensor has failed. The question is why does the MIL only come on above 70mph. The answer lies not in the sensor but how and when the sensor is tested by the PCM. Every sensor (and actuator) in the engine control system is tested by the software, but not all the time. Each sensor has its own set of test entry conditions; each OEM ...


5

While the fault code that popped the MIL is tremendously useful by itself, freeze frame data offers huge help, as it allows you to see the exact conditions under which the engine decided that there is a fault. You will know at what RPM the code was popped, what the engine load was, whether the engine was warm and in closed loop mode, if it was overheating, ...


5

To add to the list, run the engine without the fuel filler cap on.


4

Not all DTC's will activate the CEL It is up to the manufacturer whether or not to trigger the Check Engine Light based on the Diagnostic Trouble Code, so a misfire DTC is not the treated with the same severity as an idle-control DTC. In fact, the same make and model manufactured for different markets (Europe vs US) can have sets of triggers, as is the ...


4

I haven't been able to find any solid conclusions on the VW forums regarding the root cause for this behavior, but there are some clues as to what could be causing this from the diagnostic code. Fred Wilson's answer remains a distinct possibility but I struggle to reason with why the engine computer would choose to throw a code/MIL for a bad sensor on a ...


4

The diagnostic systems in cars get upgraded every few years. It wasn't until the early 2000's that car manufacturers really started to integrate ways of displaying diagnostic info without an OBD scanner. Typically if it is not included in the shop manual it is not a feature on that car. Your best bet is to go to the local autoparts store or shop and have ...


3

I have a 2001 Pontiac Sunfire that HAD a similar issue. After having been looked at by far too many people, one mechanic figured out how to recreate the issue by pouring water on a certain part of the engine while running (sorry I'm not sure where exactly), but even that didn't shed much light on the issue since it was supposed to be acceptable to do that. ...


3

The P0420 and P0440 are completely unrelated (other than both being related to emissions). The P0420 is having to do with catalyst function. The P0440 having to do with EVAP system. There is no way for one code to have morphed into the other code. P0420 can appear and disappear over time due to the nature of what is being seen by the computer. If the after ...


3

We find FF so useful that we retain it on the customers invoice in case the same code sets later. It is also very helpful when used in conjunction with a test drive on intermittent faults. It tells exactly how to duplicate the conditions under which the fault set. There are times when its limit of setting on only one code is frustrating because it is not ...


3

They help us home in on what might be the root cause Maybe an example would help explain why freeze frames are so useful Here is the P0300 freeze frame from that infamous Merc GLK280: +-----------------------------------------+-------------+ | Fuel System 1 status | 1 | | Fuel System 2 status | 1 | ...


2

very well formed question. At any point did you test your fuel injectors? if you got some crud in your fuel line one injector on one side might be dripping while another might be going rich. Does any of your spark plugs look white or black. I would expect to see a white one on bank one somewhere and a black sooty one on bank 2 some where. Can you hear any ...


2

Because this issue is speed dependent, I'm almost certain that it is related to exhaust gas temperature. Paulster2 suggested checking whether the issue happens at a lower gear. However, then the load on the engine is lower, so there are less exhaust gases. It may be the case that the issue does not happen at a lower gear, therefore. But a good idea to check ...


2

We can still read the code without a code reader with a key dance. Some people said the e-brake must be on in order to do this but the main problem in my case was about the key dance itself. Basically, there's 4 ignition key positions: Off Accessories Run Start When I was doing the key dance, I was doing it between position 1 and 3. However, I just ...


2

I own a 2003 2.0 Jetta which has the same issues. Upon further study and inspection I find that when there is moisture in the air, either raining or dense fog, the car either will be hard to start or will not start at all. When I pop the hood I notice that ALL of the electrical components in the car have condensation on them. For example, even though the ...


2

DO NOT PAY SOMEONE TO RESET THE BLINKING AIR BAG LIGHT!!!!! Open the driver’s door. Note the rubber covered button located low on the B pillar, a button which is pressed by the door when the door is closed. This is the Driver’s Door Switch (DDS). Turn the ignition from OFF to ON. Press the DDS at least 5 times within 7 seconds after turning the ignition ...


1

The gas or petrol cap is a good idea. Removing the coil pack(s), on cylinder 1, is another one. Sometimes you can easily find an electrical connector - say the O2 sensor - and disconnect it. This, of course, depends on what connectors are easily reachable. On a Hyundai Coupe, the O2 sensor is easily accessible.


1

The easiest thing I can think of is to remove the gas cap and start the engine. You should quickly see a MIL. The scan tool should report something like Evap emission fault large leak.


1

Bad idle or auxiliary air valve of some sort. Cold-air valve, idle-up solenoid, EGR valve.


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