Test 53 is the oxygen sensor validation test. If the pre dive test fails on this test, is because the primary oxygen sensor returns a value that is outside the allowed range, indicating a problem with the oxygen sensor.
There are a few things you can do, to check if the sensors are bad or not:
- Swap place between the primary & secondary sensor and run the pre dive again.
- If it's cold, warm the sensors before doing the pre dive or do the pre dive indoors.
- If you have put brand new sensors in to the unit, allow the new sensors to breath for 24 hours before you do a pre dive test with them.
- Analyze the gas you use, to make sure the levels of oxygen are correct.
If the unit continues to fail on test 53, replace one or both oxygen sensors.