P0355 is a generic OBD II diagnostic code that indicates an issue with the ignition coil “E”. Specifically with the primary or secondary wiring circuits. If your Audi Q8 has thrown this code, it may be accompanied by P0305.
P0355 is a relatively straightforward diagnosis and is typically caused by a bad coil pack or wiring harness issue, although other factors can cause it. We’ll cover the most common ones directly below.
P0355 Symptoms: Audi Q8
- Check Engine Light– The check engine light may be all that you notice when you have this code, particularly if it is caused by an intermittent wiring issue with your Q8.
- Misfiring– P0355 might be accompanied by P0305. P0305 indicates a misfire in the fifth cylinder. Resolving P0355 will typically clear P0305 as well. Misfiring can lead to a lack of power and/or engine hesitation. It can also really mess up the catalytic converter.
- Rough Idle– Your vehicle may idle rough if the fifth cylinder isn’t getting enough spark. You very well may smell raw fuel as your Q8’s engine runs as well.
Understanding Primary and Secondary Wiring
It’s essential to determine if it is the primary or secondary circuit that has thrown the code. Luckily, it’s easy to determine which one is at fault. Use the swap test method listed directly after this section.
Primary
The primary wiring is the wiring harness leading from your Q8’s ECM/PCM to the ignition system itself. A short, open, or poorly ground wiring harness is almost always what causes P0355 when the primary wiring side has thrown the code.
Secondary
The secondary side of the equation is the spark side. The spark side is the plugs, plug wires (if so equipped), or the spark plug itself is causing your Q8 to throw P0355.
Ignition Coil “E” indicates the problem is in the fifth cylinder. Next, you’ll need to look up which cylinder is number five on your engine. Different manufacturers use different methods. Here’s a pretty good explanation of how how to locate cylinder 5.
P0355 Diagnosis Tip “Swap Test”
There is a straightforward test to determine if the primary or secondary wiring has thrown this code in your Q8. First, move the ignition components (coil pack, plug wire, plug) from cylinder 5 to another and clear the codes.
If the code moves from the fifth cylinder, You now know it’s the spark plug, coil pack, or plug itself. You can keep doing this until you lock down the exact cause. For instance, now that we know it has to be one of the components you moved, move them again, but leave one behind. Once the code stops moving with the parts, you know you’ve found the problem.
P0355 Causes: Audi Q8
These are the most common problems that cause P0355:
- Wiring Issues (short, open, or bad ground)
- Bad Coil Pack
- Loose Connection at the coil
- Bad PCM
P0355 Diagnosis: Audi Q8
The first goal of diagnosing P0355 is determining if you are dealing with a primary or secondary wiring problem in your Q8. If you do that, you’ve eliminated half of the variables.
Voltage Test (Optional, but time-saving)
The first place that you would want to start looking for what could be causing P0355 in your Q8 would be the wiring harness. You can use a digital voltmeter to check if the coil pack is getting the proper signal. You would want to set it for A/C hertz and check to see if it is between 5-20hz.
If it was between 5-20hz, it’s doubtful that the coil pack has gone bad. Although, it could be a bad plug or plug wire as well. If it has no signal, it’s time to look at the wiring harness. If you don’t have a voltmeter, you can use the parts swap method to help you determine if it’s the primary or secondary side causing your problems. See directly below ↓.
Parts Swap
A great way to determine if it is an ignition-related component and not a wiring issue is to reset the trouble code and swap the coil, plug, and plug wire (if equipped) with another cylinder.
If the misfire “jumps” to the cylinder that you’ve just swapped your Q8’s ignition components into, then you know that what you are looking at is a coil, plug wire, or (most likely) coil pack failure.
If the misfire did move cylinders, you can go ahead and replace the plug, plug wire, and coil pack. If you are on a tight budget, you can keep resetting the code and swap the ignition parts back one at a time until the misfire returns to cylinder 5. Start with the coil pack. The swap method is covered more in-depth in the section above.
Wiring
If the misfire failed to move from the fifth cylinder, then you know that you most likely have an issue with the wiring harness going from the coil pack to your Q8’s PCM/ECM.
First, take a look at where the harness plugs into the coil pack. Is it damaged or loose feeling in relation to the other cylinder’s connections? If so, you may need to replace the harness plug and pigtail.
If the misfire is intermittent, jiggle the wiring harness and see if it impacts the way the engine is running. If it does start or stop misfiring, you know you’ve found your problem.
Look anywhere that the harness bends or touches anything sharp. Look to see if it looks burnt anywhere. Check for damage and repair the wiring accordingly.
Make sure that it has a solid ground.
PCM/ECM
If you still can’t find the problem, it’s time to take a look at the PCM. PCM issues are the least likely answer and an area where it may be time to call in the pros.
Wrapping Up: P0355 Audi Q8
P0355 is usually pretty easy to diagnose through the swap test, even if you don’t have any special diagnostic tools. If there is anything you can add, please leave a comment below. Good luck fixing your Q8!