The check engine light / engine management light on my Honda CR-V came on recently. Then it went off…then it came back on again…then it went off again. You can probably guess what happened next. In this post I’m going to describe how I worked out what was causing the light to be on, what had gone wrong (knock sensor) and how I fixed it (replaced the sensor).
The car in question here is a 2004 Honda CR-V with the 2 litre K20A petrol engine. This engine is found in lots of other Hondas (Accord, Civic, Stream Stepwgn), so hopefully this information will be useful for lots of people.
Obvious and less obvious clues something was wrong
Clearly the obvious clue was when the engine management light came on. Now I’ve fixed it, I realise the Honda had been giving me subtle clues that something wasn’t right for some time before the light came on. It wasn’t driving quite as it should, but also wasn’t quite bad enough or annoying enough to make me notice. Having fixed the problem, I now appreciate there was a slight hesitation when starting to accelerate from idle.
Finding the cause
When the light first came on I stopped as soon as I could to check for obvious signs (or smells) of woe under the bonnet and under the car. I suggest you do the same if this happens to you. In my case, everything was fine.
At this point I knew I needed to reach for a code reader. I used a Foxwell NT200 diagnostic scan tool.
This is a very cost effective unit but there are a couple of things to be aware of:
- It can only deal with ECU codes (i.e. not airbag, ABS or other electronic modules).
- It doesn’t do JOBD, so isn’t suitable for use on Japanese import cars. JOBD is a version of OBD2 for cars sold in Japan. Check before buying a code reader if you want to use it on an imported car!
Neither of these things were relevant in this situation.
If you haven’t used one of these code readers before, it is very simple:
- Find the OBD2 port. In this case it is in the driver’s footwell, above and to the left of the clutch pedal.
- Plug in the reader.
- Switch on the ignition.
- The code reader gets power from the car, so doesn’t need its own power.
- The code reader will communicate with the car’s ECU and report back on whether any codes are stored. It isn’t completely automatic so you’ll need to click through a few menus. This reader only has 2 buttons so you can’t go too far wrong.
- Navigate through the menus to read the code(s).
I was hoping to see a single code show up on the screen rather than a handful of codes, which can be more difficult to diagnose. Thankfully I was ‘rewarded’ with a single code – P0325, which refers to a fault with the knock sensor.
What is a knock sensor?
We should probably start by covering ‘knock’ itself. It is also known as pinking and refers to the noise produced when the air fuel mixture in the cylinder ignites at the wrong time (i.e. not in response to the spark from the spark plug).
If this keeps happening it can be bad news for your engine.
This is why engines have a knock sensor. This is bolted to the engine block and basically listens out for knocking. When detected, the ECU adjusts the ignition timing or air fuel ratio to stop the knocking.
Fixing Honda P0325 Code – Replacing the Knock Sensor
- Start by putting the car on some ramps so you can get underneath. A jack and axle stands will be fine too, but I find ramps quicker for jobs where I don’t need to take the wheels off.
- Lift the bonnet and remove the plastic tray underneath at the front. Be careful with the trim clips, but some will probably break anyway. You can use cable ties as a temporary fix if you need to wait for more to arrive.
- Find the knock sensor. It’s in a slightly tricky position on the front of the engine block. The internet is peppered with attempts to video and/or photograph its location. Here is mine! I this gives you a rough idea of the location. The picture was taken with the undertray removed.
- Check the wiring and the existing knock sensor are secure, so you don’t waste money on a new sensor if there is a simpler solution. In my case, they were, so on to the next step…
- …which was to research the likelihood of a fault with another component causing this Honda P0325 code. This is the second part of ‘trying not to waste money buying unnecessary sensors.’ I didn’t find a great deal of information to suggest this, so set about sourcing a replacement.
Time was not on my side – I was going on holiday in 2 days so didn’t really have time to order online and wait for delivery. So I contacted my local Honda dealer and was surprised to hear they had one in stock. This confirmed that faults with this knock sensor are common: they wouldn’t keep one in stock unless they sold / replaced quite a few. We won’t talk about how much it cost!
On to the replacement procedure. The instructions could be summarised as follows:
- Disconnect wire.
- Undo old knock sensor.
- Screw in new knock sensor.
- Reconnect wire.
Fairly straightforward then? Yes and no, depending on your patience, dexterity and the size of your hands. Let’s go through the procedure for Honda knock sensor replacement.
- Disconnect the battery negative terminal.
- Make yourself a coffee / tea / drink of your choice.
- Use hands or angled long nose pliers to release the wiring connector from the sensor and remove it. I did this bit with my hand, but this is tricky because you can’t see what you’re doing!
- Loosen the sensor with an open ended 27 mm spanner. You could also use a 27 mm socket with a universal joint on the end, but you may need to have the UJ only partially inserted into the socket, to give space for the electrical connector on the sensor. I used this job as an excuse to treat myself to a lovely Facom 27 mm spanner, which was a pleasure to use.
- Make sure the sensor mating surface on the engine block is clean and flat (i.e. remove any grease and rust).
- Screw the new sensor into position by hand.
- Tighten the new sensor to 31 Nm.
- Reconnect the wire to the sensor, making sure the connector clicks into place.
- Reconnect the battery.
At this point you can start the engine and (hopefully) enjoy the lack of engine management light on your dashboard. I connected my fault code reader prior to starting, fully expecting to have to delete the P0325 code, but it had already gone. This was a good result. Time to put the undertray back on and go for a test drive.
Honda P0325 Code Summary
We’ve now been through how to identify the Honda P0325 code as a cause of the engine management light coming on. We’ve looked at how to fix the issue by replacing the knock sensor, using the popular K20A engine in a 2004 Honda CR-V as an example. I found this a very satisfying fix. As well as getting rid of the engine management light, and any concerns about engine damage, it actually improved the driving experience too. There may have been a marginal improvement in fuel consumption, but it is difficult to say for certain because fixing this problem coincided with warmer weather.
I hope this information was useful for you. If anything wasn’t clear or if you’ve got a question, why not post a comment below?