P0302 in the Mazda BT-50 is a common OBD II trouble code. It indicates that your truck’s second cylinder has a misfire.
P0302 is a real drivability concern and should be dealt with right away. If it’s bad enough to cause your BT-50’s check engine light to come on, you shouldn’t drive your truck at all.
Repairing P0302 should be considered a high priority. Unlike a lot of the OBDII codes, this code has to do directly with engine combustion. It also can cost money to ignore it, since driving with a misfire can damage the BT-50’s catalytic converter.
The most common fix for P0302 is to replace the spark plugs, coil packs, or (if equipped) plug wires.
Table of Contents:
P0302 Meaning: Cylinder 2- Misfire Detected
P0302 is a cylinder-specific misfire code, meaning it’s only the second cylinder that has a misfire. But, where is the second cylinder?
On “V” configuration engines, it’ll usually be the first cylinder on the head further back from the front of the engine. A quick google image search will confirm the correct cylinder (include your BT-50’s model year and engine type).
In order for an engine to burn fuel efficiently, each cylinder needs:
- Fuel– In the right quantity (around 14.7 parts air to one part fuel).
- Air– It needs to be metered by your BT-50’s mass air flow sensor or MAP sensor, so the powertrain control module (PCM) knows exactly how much air to let into the combustion chamber.
- Spark– The spark plug needs to fire at the right time and at the right temperature.
- Compression– The air-fuel mixture must be compressed during the engine’s power stroke.
If one of the above variables is off, your BT-50’s second cylinder will misfire, or it won’t fire at all.
BT-50 P0302 OBDII Code Symptoms
Here are the most common symptoms of P0302 in the Mazda BT-50.
- Check engine light
- The truck itself may begin to run rough. It depends on how serious the misfire is.
- Your BT-50 may produce excess vibration, especially at lower RPM.
- Fuel mileage may suffer.
- You may smell raw gas coming from the tailpipe.
- The engine may backfire.
P0302 Trouble Code Causes: Mazda BT-50
There are quite a few things that can cause the P0302 trouble code to trigger in the Mazda BT-50.
Here are the most common problems that may cause misfiring. They are presented somewhat in order from most to least likely to be causing P0302:
- Bad Spark Plugs– A fouled spark plug is the most common cause of P0302. Look at the electrodes and see if they are in good shape. Your BT-50 likely has iridium plugs that need to be changed very infrequently. That being said, a bad spark plug is the number one offender when it comes to P0302. Here’s a great video on verifying a spark plug is bad.
- Spark Plug Wires– On most modern engines, the plug wires are not nearly as long as they once were (if your truck even has them), but they can still go bad. Here’s how to tell if your plug wires are bad (video).
- Coil Packs– Coil packs rarely go bad, but when they do, they can cause P0302 in your Mazda BT-50. Replacing a set can be very expensive. Here’s how to test them.
- Bad Fuel Injector– If you have a fuel injector that has failed, it won’t be able to properly atomize fuel, and you’ll get P0302. Here’s a good video on how to diagnose an injector; it can be a little tricky. You’ll likely see P0171 and/or P0202 with a bad injector.
- Vacuum leak– If your BT-50 has a vacuum leak, it can be difficult for the PCM to get the right air/fuel mixture. This will cause the cylinders to misfire, and it’ll throw P0302 if the leak is around that specific cylinder on the intake manifold. Popular Mechanics: How to find a vacuum leak. You’ll likely see P0171 and P0300 when there’s a vacuum leak.
- Cam or Crank Sensors– This one is unlikely, but it does happen. If the ECU is not getting the right signal from these sensors, the vehicle’s timing will not sync up, and it’ll misfire. You’ll likely get P0300 and a cam/crank correlation code too.
- Mechanical Issue– If your BT-50 has a leaking head gasket, bent valve, cracked head, etc… that would cause compression to not be as high as it should be, you’re going to get P0302. You should also feel that your truck is down on power as well.
P0302 Fix: Mazda BT-50
If P0302 is the only code you get when you plug an OBD II scanner into your BT-50, this section should help you determine what is causing the code.
If you have multiple codes with P0302, jump down a section.
1. Swap Test
Here’s a quick and easy test to determine what is causing your BT-50’s second cylinder to misfire. Swap ignition parts to another cylinder. Here’s how to do it.
- Identify the second cylinder.
- Remove the spark plug.
- Swap it with the most convenient cylinder to access’s spark plug.
- Clear your BT-50’s DTC codes with a scanner.
- Start the engine and wait for the check engine light to come back on. If it changed to a different P030X code, the plug was bad.
- If nothing changed, do this for the coil packs and plug wires (if equipped).
- If the code stays P0302, you’ve ruled out ignition-related issues.
Here’s what to look for when the swap test didn’t change your truck’s misfire code number.
- Check the wiring harness going to the cylinder two coil pack. If it’s damaged or loose, repair it. Ignition wiring is a common rodent damage area.
- Check for a vacuum leak.
- Verify the second injector is working (there’s a link to how to test one above).
- Do a compression test.
- Perform a leak-down test.
P0302 + Other Codes
P0302 + P0300
The most likely reason your BT-50 will get P0300 and P0302 simultaneously is faulty spark plugs.
P0300 in the Mazda BT-50 indicates random multiple misfiring, which means that multiple cylinders are misfiring at the same time.
If your Mazda BT-50 has P0300 and P0302 error codes, it’s best to diagnose why the second cylinder is misfiring and see if that will fix the P0302 code.
Try doing the swap test from the previous section. Make note of the condition of BOTH spark plugs as you swap them. If they look fouled, new plugs will likely clear this code.
P0302 + P0171
Look for a vacuum leak around the second cylinder or a bad fuel injector.
P0171 is one of the most common trouble codes there is. While there are many potential causes for P0171, the most prevalent is a vacuum leak.
When your BT-50 has P0302 and P0171 together, it’s often caused by a clogged or underperforming fuel injector.
P0302 + Other Cylinder Misfire Codes
Treat P0302 with these codes like it has P0300.
P0302 will often be accompanied by codes P0301, P0303, P0304, P0305, etc… These codes indicate a misfire in cylinders one, three, four, and five, respectively.
Treat P0302 with these codes like it has P0300. Suspect an ignition-related cause or a vacuum leak.
Is P0302 a serious concern?
P0302 is cause for concern and, left unfixed, can leave you stranded. Your BT-50 will be virtually undrivable if the second cylinder stops firing altogether. The raw fuel can also damage the catalytic converter.
Can you drive your BT-50 with P0302?
We do not advise driving your BT-50 with P0302. It can cause damage to your truck.
Is P0302 hard to repair?
Most of the time, P0302 is not hard to repair, as you’ll be swapping out ignition parts. It’s a great first-time project for a shade tree mechanic. If the problem ends up not being ignition related, that’s when you might have to bring it into a shop.
Replacing the spark plug or coil packs is the most common fix for P0302 in the Mazda BT-50. There are other causes, but the swap test can help narrow them down considerably.