Oil pressure sensor solution - Page 1
Forum section: electronics / beginners

author: Veketti
author_rank: Regular Contributor
timestamp: August 18, 2025, 06:30:10 pm
content: Dear All,My car doesn’t have oil pressure sensor, instead it has switch which opens at 0.4bar. I’m planning to build pressure meter and small discreet display to dashboard. I’m aware of the VDO oil pressure senders which come in varied configurations that could basically be swapped in place of original switch and have both switch and variable resistor for pressure. However, these are pretty big and, in my case, won’t fit in place of the original switch.My idea is to replace the original switch with small Honeywell PX3 industrial pressure sensor. Then to create the original switch functionality, I was thinking to add to the PCB small SPDT relay and connect the original switch cable to the NC contacts. Then by microcontroller code control the coil when pressure is above 0.4bar. This way I’d have potential free contact to replicate the original pressure switch.However, this sounds quite complicated and I’m not sure is it good idea after all, as there’s quite many things that can go wrong and lose the original functionality…I’d appreciate your thoughts / suggestions. Thank you.

author: jpanhalt
author_rank: Super Contributor
timestamp: August 18, 2025, 07:03:06 pm
content: Try disconnecting the sensor and see if the car still runs. It's likely a newer car won't run.* If that's the case, and assuming you can't modify the ECM code (or whatever your car has attached to it), then you probably need to duplicate that part's actions. I would look to see whether there is another access port for the oil pressure and leave the factory system alone.* I have a field sprayer with a 5HP Kawasaki engine and oil pressure sensor. That was simple to bypass, but I suspect any car that is less than 40 years old won't run.

author: bostonman
author_rank: Super Contributor
timestamp: August 19, 2025, 02:13:37 am
content: QuoteMy 97 Buick works without the sensor. I may be wrong and it has two sensors (one internal to the engine), but I've disconnected the external one and (if I remember correctly) tied the wires together.The sensor was giving me issues. One time it leaked, another time it gave false low oil, etc... I got fed up and disconnected the sensor.At this point though the car has enough idiot lights on that I may need a higher amperage alternator to illuminate all of them.

author: Poroit
author_rank: Frequent Contributor
timestamp: August 19, 2025, 09:04:59 am
content: G'day Veketti,Do you have space to add a T Piece so you can retain the switch and add a compact pressure transmitter?https://au.omega.com/pptst/PX190.html

author: jpanhalt
author_rank: Super Contributor
timestamp: August 19, 2025, 09:28:54 am
content: Let me clarify, if you can make the car run without the idiot light sensor or a check engine light coming on, why try to duplicate its action? You'll have a gauge. For years, that was sufficient alone and still is in many applications.

author: bostonman
author_rank: Super Contributor
timestamp: August 19, 2025, 12:26:47 pm
content: QuoteGreat point!In my case, I don't believe my oil pressure light has worked since hacking the connector about a decade ago.Actually, at the time when the light came on, I knew the oil was full, I didn't see any oil leaks, etc... My conclusion was: the sensor/cable is broken or the oil pump is failing. Due to the age of the car, condition, etc... I wasn't replacing the oil pump and drove the car home; end result was a failed sensor.

author: BILLPOD
author_rank: Frequent Contributor
timestamp: August 19, 2025, 02:08:26 pm
content: Good Morning Veketti, As Poroit suggests, install a Tee fitting and install a mechanical gauge right there on the engine, (you may also need some other fittings, like an elbow.) Here's one on Amazon:https://www.amazon.com/Equus-6234-Mechanical-Pressure-Gauge/dp/B000EVYHN6/ref=asc_df_B000EVYHN6?tag=bngsmtphsnus-20&linkCode=df0&hvadid=80333198183626&hvnetw=s&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=105222&hvtargid=pla-4583932719133231&psc=1.Those mechanical gauges are a lot more accurate/dependable than most electronic sensors, with only a warning light. You might even want to plumb it through the firewall and mount the gauge on/under the dashboard. That's my suggestion. I wish you success

author: Veketti
author_rank: Regular Contributor
timestamp: August 24, 2025, 07:46:26 am
content: Thank you all. Excellent suggestions! It’s relatively modern diesel engine and it actually has two pressure switches. Due to emission crap it has valve which keeps the oil pressure low at below 3000rpm. So, the ecu monitors both pressures. I just noticed that the low-pressure switch is NO contacts so ECU monitors it and not directly connected to the idiot light. I recall hearing from some local respectable garage youtube channel that the present of oil pressure is only monitored when the engine speed is over 1500rpm. Crazy, huh.edit: I found that mention. It was so that from startup, the presence of oil pressure is only measured after the rpm has reached 2000rpm first time.I ordered Y-adapter and hope that there’s enough space for both, the original switch and PX3 sensor. Got the PCB designed and populated it with small signal relay just in case I can’t get that Y-adapter there. I’ll make sure I have both approaches ready when it’s time to install it as there is quite much things to disassemble to get to the switch.

author: bostonman
author_rank: Super Contributor
timestamp: August 24, 2025, 01:18:09 pm
content: QuoteI meant to elaborate on my message above. It was suppose to imply: I'm uncertain if I have an internal oil pressure/level sensor along with the existing (but disconnected) external oil "sender" switch.Looking at the idiot lights, I only see one oil light, so I assume my car only has the one. In the past I had the external oil sender leak, it got replaced with an aftermarket, that leaked, so an OEM was used, and then the connector got lose. Since I know enough to monitor the oil level myself, it made sense to just disconnect the connector which doesn't trigger any computer issues in my 97 car.Due to the age of the car, if the oil pump goes and the disconnected oil sender doesn't alert me, then so be it. I'm not replacing the oil pump, so the need for the oil sender to be connected was meaningless.

author: u666sa
author_rank: Frequent Contributor
timestamp: August 24, 2025, 01:42:08 pm
content: Quote from: Veketti on August 18, 2025, 06:30:10 pmI highly advice you go a different route. Leave the stock sensor in place. It does a specific job, specific sequence of events relies on it. Instead, install a separate oil pressure sensor and a pressure gage. But one from a tuning shop or on amazon or on aliexpress. All it work just fine. You'd need a kit with sensor and gage, and then also a gage place holder for your specific car. Be it on a pillar, in dash, in a vent, center console, etc.