So, a few days ago I went to get a smog test (thanks CA) to register my 2003 S40 I just bought from a friend from work. It passed the smog portion of the test but the "Check Engine" part of the test failed and brought up 7 different codes. After much searching on here and other forums and google in general I have somewhat of an idea on what is wrong. I would like other opinions and options, as I said I have searched all over google and think that you guys are very helpful.

P0128- Coolant Thermostat (Coolant temp below thermostat regulating temp)
I think that it might be a simple issue of replacing the thermostat, in which case should be very easy and cheap.

P0171- System too lean Bank 1
P0237- Turbocharger/Supercharger Boost Sensor "A" Circuit Low
I looked into these problem separately and was coming up with nothing, but then I found that when combined could be the MAP sensor.

P0302 and P0304- Cylinder 2 and Cylinder 4 Misfire Detected
At first I though that it could be the 4th cylinder ignition coil going bad, but the 2nd and 4th cylinder arent connected.

Upon looking further into the problems maybe all four of those codes could be a result of a bad MAP sensor (But wouldnt that effect all four cylinders misfireing?) But that is my working theory at the moment, like I said I'm looking for other opinions or something that could help me.

P0700- Transmission control system (MIL Requested)
P0705- Transmission range Sensor "A" Circuit (PRNDL Input)
Looking at these together the only thing that I could figure out is the PNP Sensor is the problem. (I havent had many problems with the transmission though, every once in a blue moon putting it into drive or reverse causes it to jolt, and one point the arrow flashed for a day but stopped) Any insight into this problem and how to fix it would be appreciated.


If anybody has any ideas on how to help me I'd greatly appreciate the help. Also, I'm trying to do this without a mechanic, and I'm very limited on tools and money. So, the best way to do this without having to spend the most money is very well appreciated.

 

You may want to measure your ECT sensor or just replace it when doing the thermostat (since you need to pop the thermostat cover off to access the sensor anyways). For the transmission codes you can try doing the "shifter row" to see if that gets the PNP to clean up a bit (run the shifter from Park to Lo about 20x fast). In terms of the MAP, you can try cleaning up the intake and the sensor before replacing (avoid carb cleaner, use a product like CRC MAP Cleaner ~$6 ) The misfires can also be due to the plugs as well - these cars are somewhat sensitive for some reason (go with OEM or copper cores). If you are lucky you may be able to clear the codes and do some of these quick fixes and be good to go.

 

Okay, I'll give it a shot. Also, is the PNP and the Neutral Safety Switch the same thing? One other question that I have is how to rest the computer codes. I've read disconnect the battery completely for 10 minutes, an hour, a few hours, or just disconnect the negative terminal and turn the key 3 times then reconnect the terminal. What is the best and most effective way.

 

pnp switch is short for the park neutral position sensor. It plugs into the starter circuit to not allow you to engage the starter when the car is in gear... and if it goes you have odd issues like no start, or can't get the key out etc. Computer codes need to be cleared via an OBD2 reader. The easy way is to go to a big box auto parts store like Autozone or a friendly local indy and ask if they can read/clear the codes for you. You will want to write them down because if something is wrong, the codes will just reset. Plan B would be to buy a code reader - eBay/Amazon/HarborFreight etc... They come in a range of prices and compatibility - some can only read/clear power train codes some can do all the codes (chassis etc).