Intermittent MIL, no stored codes?

[SWFL_NSX]

Hello All,

I've noticed a MIL twice while driving my 92 in the past few weeks. Both times it went away after I turned the car off and restarted it.

Today I used a paperclip to jump the blue connector in the passenger's foot well, but when I turned the key to "on" the MIL illuminated and then turned off as it normally does on startup.

Are there some faults that do not store codes? Did I miss a step in the diagnostic procedure?

 

[SWFL_NSX]

Solution

After posting this to FB Kaz chimed in with the solution-despite trying two different paperclips I was still not making proper contact inside the blue diagnostic connector. Assuming there were no codes stored and the jumper was jumped correctly the MILwould simply stay on/lit...since it was turning off the issue had to be with my jumper or perhaps the wiring of the connector.

I tried backpinning the connector and was able to read the codes via the MIL-Code 43 for a front 02 sensor. Since the fault is currently intermittent I'm going to try to buy an oscilloscope so I can check the wave forms on a sensor that is throwing codes vs a sensor that isn't.

 

[Old Guy]

As an observation, unless you want an excuse to buy an oscilloscope (personally I am guilty of any excuse to buy a new tool), buying an oscilloscope to diagnose an O2 sensor makes for a fairly high cost diagnosis. Even USB based scopes that plug into a laptop are at least $100 for a basic good one. If you have a basic digital voltmeter on hand, the input impedance is typically high enough to avoid loading the sensor allowing for a sensor voltage measurement. The down side to the digital voltmeter is that on a working sensor the voltage is typically fluctuating when the engine is running. Because of the lax sample rate on less expensive digital voltmeters all you get is a bunch of flashing numbers which is unintelligible. However, if the voltage on a running engine at operating temperature reads a steady 0.1 or close to 1.0 volts, you can bet that the O2 sensor is dead or you have a really serious fuel mix problem which would materialize itself as a driveability problem. The service manual sets out a good basic procedure for trouble shooting code 43 with a voltmeter with the advantage that it is not on a running engine..

However, if you are looking for an excuse to buy a scope, go for it.

If you confirm that it is the O2 sensor that has / is failing and you are still running on the original O2 sensors, consider replacing both front and back sensors at the same time while you are under the car. On a clean running engine narrow band sensors are pretty durable; but, they do eventually fail.

 

[SWFL_NSX]

As an observation, unless you want an excuse to buy an oscilloscope (personally I am guilty of any excuse to buy a new tool), buying an oscilloscope to diagnose an O2 sensor makes for a fairly high cost diagnosis.

Agreed! I've been wanting to buy a scope for a while...I've convinced myself that a DS203 or 213 is a good place to get started. It's just an excuse to pull the trigger :smile:

Between the code 43, the exhaust smelling richer on startup, and the mileage (100k) I'm comfortable with replacing both sensors.

If you have any input on this scope, I'm all ears. Electrical/electronic issues are not my forte, but I'm trying to get better.

https://www.banggood.com/MINI-DS213...Inch-Screen-With-Logic-Trigger-p-1412378.html

 

[Old Guy]

Agreed! I've been wanting to buy a scope for a while...I've convinced myself that a DS203 or 213 is a good place to get started. It's just an excuse to pull the trigger :smile:

Between the code 43, the exhaust smelling richer on startup, and the mileage (100k) I'm comfortable with replacing both sensors.

If you have any input on this scope, I'm all ears. Electrical/electronic issues are not my forte, but I'm trying to get better.

https://www.banggood.com/MINI-DS213...Inch-Screen-With-Logic-Trigger-p-1412378.html

Sent you a PM with comments on scopes since most forum members are probably not interested in a scope selection discussion.

 

[Larry Bastanza]

MIL code 43 is Fuel System - Front bank.

I would check fuel filter(fuel pressure test may tell a lot) , clean fuel injectors, replace spark plugs.

JMO,
LarryB

 

[SWFL_NSX]

Thanks Larry. Injectors were cleaned about 18 months ago, plugs replaced around same time frame.

I'll add fuel filter to the list-I don't have previous service records and it looks original.