Last weekend I replaced some original sensors in my 2002 BMW E39 M5. Scandinavian Import Servicenter in Rockville, MD kindly invited the DIY program back into their beautiful facility. Last year I replaced my power steering hoses and reservoir at the same location. This time I needed to replace some sensors that were original to the car.
Headlight Sensors
The first issue was that my new Euro headlights were not leveling properly. Most of the time they were pointing too low. There are multiple reasons why this can happen, but my Foxwell NT510 scanner confirmed it was the front leveling sensor connected to the passenger side control arm. I had to reconnect this sensor back in 2013 when work had been done replacing front control arms and the shop forgot to reattach it.
Ryan Schultz’s E39Source is a great resource for all things E39 and his video on replacing the sensor was hugely helpful. He often goes overboard and in this case replaced the entire bracket the sensor connects to, I only did the sensor and the sensor arm:
Rear O2 Sensors – I Hope
The second fault reported on the scanner was more ominous. I got catalytic converter faults bank 1 and 2. That would be a very expensive replacement. But after researching I was reminded that the rear 2 oxygens sensors on the M5 only monitor the catalytic converter. So if they fail, the error message would read the converter when often it’s just the sensors.
I also remembered these sensors are almost certainly original. In 2011 I had replaced the front two O2 sensors, which measure air/fuel mixture. But I didn’t touch the back ones. So there was a good chance (fingers crossed) that 20+ year old sensors had died and not the converter.
Once again there was an E39Source video to review. My job was much easier than their video because I was able to put the car on a lift, and also had the special O2 wrenches from the earlier job.
O2 sensors are an easy job on the E39. As you can see in the video and the pictures below they are right there when you raise the car. It’s also not bad on the wallet if you buy the sensors directly rather than through BMW. I paid $72 each for the sensors from FCP Euro – the BMW cost was $324!
I was going to do one more sensor during the DIY, a temperature sensor that sits on the lower hose going into the radiator. The reason I didn’t was a good example of the benefits of having pros around you when doing these jobs. Replacement looked pretty simple but when I asked shop mechanic Vincent about how best to remove it he said:
“You know you’re going to lose most of your coolant if you do that, right?”
No I didn’t! In fact I had read a post on M5Board that very little coolant would be lost. But I wasn’t going to debate a professional and risk making a huge mess in his shop. That E39 M5 sensor replacement can wait.
I scanned the car again and both faults are gone. Pics below – enjoy your Thanksgiving!
UPDATE 1/8/23 – This weekend I finished the job by installing the replacement coolant sensor. Additional research found that I could change the coolant sensor without draining the system. I took some coolant out of the expansion tank before replacing and put some rags around it. A very small amount came out.
Note for future DIYers – you’ll need a deep 22mm. half inch socket. We’ll see if this solves the issue, it could be the thermostat.
