just wondering since my ef on gas is going to the mechanics tmrw to get the head looked at, earlier a month ago had run a diagnostic check and it came up with a few errors. Codes 214 and 227 (i think) for knock sensor failure and cmp sensor input failed messages respectively.

In regards to these errors
- What these sensors are there for?
- Are they necessary that they are working
- If they dont work, what symptoms or implications may i have
- Whereabouts are they located
- How do you change them, difficulty and at what cost

Hoping the mechanic is experienced enough to know what these errors are and can fix them. Advice would be helpful.

knock sensor detects engine knock and retards timing. If this has problems, the ecu might retard timing to be safe (costing power) or might not detect engine knock (worst case = engine damage). It is near the back of the engine under the intake manifold.

CMP sensor (cam angle sensor - sits where the distributor normally sits) tells the ecu when cyl 1 is near TDC on compression stroke. If this fails your idle can get slightly lumpy and can get a little worse fuel economy.