intothelabyrinth
Active member
- Joined
- Mar 20, 2012
- Location
- Bowling Green, KY
If you have ever looked at the reviews on the common bosch sensor used for AFR gauges, you will see a lot of people complaining about how quick their sensor broke. I thought there must be a reason all these people are messing up their sensors, so I looked into it and found a pretty well researched article talking about the most common cause of early sensor failure was thermal shock from beginning to preheat the sensor before the engine was started. I decided to come up with a pretty low tech way to turn on the sensor only when the car was running for several seconds. What I ended up using was a SPDT relay, paired with a commonly available 240 A/C relay.
I power up the SPDT relay with the ignition on, and the relay coil ground is the wire for the oil pressure sender which is only grounded when the car is off. When you turn the key on the relay clicks over to the normally open output which has nothing hooked to it. Once you start the car the relay coil ground is lifted, and the relay clicks back over to the normally closed output which then supplies voltage to the input and trigger of the Volvo A/C relay. After about 5 seconds of being powered up the Volvo relay then supplies voltage to it's output which starts the wideband warm up sequence.
I will report back with my sensor longevity results once some time has passed.
I power up the SPDT relay with the ignition on, and the relay coil ground is the wire for the oil pressure sender which is only grounded when the car is off. When you turn the key on the relay clicks over to the normally open output which has nothing hooked to it. Once you start the car the relay coil ground is lifted, and the relay clicks back over to the normally closed output which then supplies voltage to the input and trigger of the Volvo A/C relay. After about 5 seconds of being powered up the Volvo relay then supplies voltage to it's output which starts the wideband warm up sequence.
I will report back with my sensor longevity results once some time has passed.