SES came on, Hi-Res Failure

[Jeanius]

Hey guys, my car has been running good with no problems, I drove it to work today no problems, then to eat with no problems, but when I got out of dinner and started her up the SES light stayed on, I waited a few min then turned the car off then back on again and it still stayed. I drove it home with no problems, I even got on it a little to see how it responded and it was fine, I hooked it up to the scanner and i got Hi-Res Failure, what does this mean? thanks in advance

[Jeff_in_Atl]

That is an OPTI error.

[Injuneer]

The engine will continue to run fine, with only a small loss of spark timing accuracy. You will not be able to tell the difference, but there may be a tiny loss of fuel economy, power and a tiny increase in emissions.

Check the harness connectors for the Opti, to insure they are not corroded or damaged.

The optical sensor in the Opti measures the crank and cam position, and feeds that info to the PCM so it knows when to fire the sequential injectors and the spark plugs. There are two position signals.

The LOW resolution signal provides a variable length pulse for each of the 8 cylinders (8 pulses per cam revolution). The PCM can tell from the pulse length when the next cylinder in the sequence will need the injector and the plug fired. The HIGH resolution signal is a series of 360 equal length pulses occuring uniformly for each one degree of cam rotation. The PCM uses this signal to measure the crank/cam position between the more spaced out LOW res pulses.

The engine is totally capable of running on only the LOW res pulse pattern. The HIGH res pulse pattern allows it to fire the injector and plug more accurately than the LOW res pulse alone, and it is this extreme measure of cam position accuracy that reduces spark scatter, providing better milage, power and less emissions.

As noted above, the PCM can keep the engine running at probably the 99% level by only using the LOW res pulse.