From Ross-Tech Wiki
18001/P1593/005523 - Altitude Adaptation: Signal Out of Tolerance
This is one of those fault codes where the ECU knows something is amiss, but cannot pinpoint the cause.
- MAF sensor (G70) out of tolerance.
- Leak in intake system.
- Throttle position sensors (G187/G188) out of tolerance.
- Check MAF/replace MAF Sensor (G70).
- Check intake systems for leaks and repair.
- Check Throttle position sensors (G187/G188).