I have a 1999 Maxima SE automatic(37K miels),the car run normal,just the air condictioner don't work. I used voltmeter to check it and I find there is no grounding at the AC relay,I read repair manual book,that grouding is control by the ECM.I also self-diagnos and I got the code 0505.
I took the car to Dealer for diagnos and Dealer say "ran diag ECM faulty not turning on AC". They estimate the repair cost around $1500.
I can find the used ECM for my Max on internet around $400,but I wonder should I get repair at Dealer or I should buy a used ECM and change it myself. If I change the ECM by myself,what should I becarefull about? Any idea.....I'll appreciated!

 

0505 means no fault. everything running properly. the ECU has nothing to do with the "air condictioner" :-)

 

dealers just want ur money, and isn't ur car under warrenty so htey should fix for free, go to another dealer

 

In what I know Nissan warranty bunper to bumper 3 years-36K miles, and warranty power train 5 years-60K miles. I don't know they still warrnty for this problem or not, but last 5 month my car had a engine light on , I took to Dealer and they said if before 2003 they still warranty fore it (that time the problem is O2 sensor and MAF sensor,it cost me around $1000)

 

The ECU does activate the Air Conditioner Relay. However, I find it VERY VERY unlikely that a faulty ECU would have everything in the car working except the AC activation control line.

So you are saying that the AC relay is not being activated? If so, you can try to bypass it and see if the AC works since that is all the ECU controls. It is also possible that the ECU is not being fed the turn on control signal.

BTW, I would find a new dealer...

 

Yes, I did try to bypass the AC relay,the AC working good,blowing cold air. Is it a goog idea if I buy a used ECM on internet and replace it myself? Thanks!

 

Check the wiring between the ECU and the A/C relay. Might have an open wire someplace along the line.