Code reader codes

[zzeekk]

These are the codes I got on my code reader. How do I fix them?

41 HEGO sensor circuit indicates system lean (right side)
61 ECT sensor has intermittently failed below 0.2 volts
91 No HEGO switching detected always lean (left side).

[BerniniCaCO3]

41 and 91 certainly suggest a failed O2 sensor on... bank 1? I think that's bank 1, which would be the passenger side.
I think it's gadget who has said he never had a failed O2 sensor throw a code, and he has had more of these cars for more years than I have had so I trust his experience.
So it's entirely possible that bank 1 is in fact, running lean. This can be vacuum leaks, more likely, or, a clogged injector that's not firing completely, or wiring to an injector such that it does not fire. At least check for the obvious (abraded wires, rodent damage).

It's bad wording, but some of these cars have "low voltage" to mean NO voltage, so in that case, it could even be a wiring issue to the O2 sensor!
That is to say, low voltage means you might actually be running lean and the sensor is doing its job. No voltage, is a wiring problem first, sensor problem next, and never going to be an actual lean condition.
"how do I fix them" isn't always so simple, is it?

Hmm... I lengthened my leads, but I remember the wires on the stock exhaust are tricky to get your hands on, otherwise I'd suggest monitoring the voltage. It'll be a good half hour's work to make a lead that'll plug into the O2 sensor so you can watch it's voltage. Or you can opt just to replace it (throwing parts at it), but the sensor is only $30 so it's not murderous. Getting it out of the stock exhaust bung hole is more murderous.


For the ECT sensor it'll be a little easier/ more straightforward. You can throw a $10 sensor at it to make you confident in the sensor itself, if the code returns, it's wiring. You can of course monitor the resistance value of the sensor as th eengine warms up, and make sure it's in range, and if it is, it is wiring.


Finally, on these cars, unplugging the battery for at least 10 min (or then touching the negative terminal to the positive to drain all little micro capacitors in the computer, thus erasing all of the memory), erases/ resets codes.
It may just be that they're ancient. Erase the codes, see what comes back?

[zzeekk]

So Why does code 91 say left side and code 41 say right side?

[86VickyLX]

Fix the code 61 first, and then retest. 41 is the drivers side 'right side' when looking into the engine bay. 91 is passenger side which is the 'left side'. Bank 1 is on the passenger side and holds cylinders 1-4. Bank 2 on driver side holds 5-8.

[zzeekk]

Where is the ect sensor located on a 1990 grand marquis?

[sly]

engine coolant temp sensor... it's on the pipe up from the thermostat (upper radiator hose on engine) housing.

[1990LTD]

FYI, coolant temp sensors tend to sit as high in the cooling system as is possible. A good starting point.

[zzeekk]

I just did another test with my code reader today and code 61 is not showing up after two test but 91 and 41 are still there