The ecm has detected failed oil level switch. where is it?

P0300 is a random misfire on all engine cylinders. check for intake manifold leaks. Here is a link to info on P0603 P0603 OBD II Trouble Code

Did you check the fuse that supply's battery voltage to pin # 16 at the DLC - diagnostic link connector ? That's where you plug your code reader in . The lighter fuse - 15 amp located in the under hood fuse box supply's battery voltage to pin #16 . The fuel gauge not working could be any one of a number of thing's , without testing an checking for DTC'S - diagnostic trouble code's I would only be guessing . Checking code's in the instrument cluster an PCM should be done by a qualified repair shop. The fuel level sending unit in the fuel tank is a direct input to the PCM/ECM - engine computer , the PCM / ECM sends this info too

The instrument panel cluster (IPC) displays the fuel level as determined by the powertrain control module (PCM)/engine control module (ECM). The IPC receives a GMLAN message from the body control module (BCM) indicating the fuel level volume. The fuel gage defaults to empty (E) if:
• The PCM/ECM detects a malfunction in the fuel level sensor circuit.
• The IPC detects a loss of GMLAN communications with the BCM.
When the fuel level is less than a certain low percentage, LOW FUEL message displays in the driver information center (DIC).

Odometer
The vehicle odometer is calculated and stored electronically in the body control module (BCM) and is sent via GMLAN to the instrument panel cluster (IPC) for display. The BCM calculates and stores the mileage based on the vehicle speed GMLAN message from the powertrain control module (PCM)/engine control module (ECM). The IPC displays the season odometer information from the BCM in the driver information center (DIC). The odometer will display error if the IPC detects an invalid odometer data from the BCM. After an invalid odometer data is received from the BCM, the IPC will display the last known odometer reading for 1.5 seconds before error is displayed in the DIC.

These can set a few different DTC'S

DTC B0158
DTC B2961
DTC P0461 (2.0L and 2.2L)
DTC P0461 (2.4L)
DTC P0462 (2.0L and 2.2L)
DTC P0462 (2.4L)
DTC P0463 (2.0L and 2.2L)
DTC P0463 (2.4L)
DTC P0464
DTC P0520


So , i suggest you take your vehicle to a qualified repair shop.

Yes the fuel tank has to come out to change the fuel pump. But are you sure that is the problem ? Your vehicle has a Fuel Pump Flow Control Module (electronic's ) Or is it just your fuel level sensor you want to replace ? And to your question of if the fuel level sensor is bad will the car shut down if the gage says it is emty but it is not? No ,this will not shut down the vehicle. You probably have no idea of the complexity of the electronic's involved an the thing's that can cause the gauge not to work .
Fuel Gage
The instrument panel cluster (IPC) displays the fuel level as determined by the ECM. The IPC receives a serial data message from the ECM indicating the fuel level percent. The fuel gage defaults to empty if:
• The ECM detects a malfunction in the fuel level sensor circuit.
• The IPC detects a loss of serial data communications with the BCM
• The BCM detects a loss of serial data communications with the ECM
When the fuel level is less than a pre-determined value, the low fuel indicator illuminates in the IPC.
Unless you have a factory or professional type scan tool your better off taking your vehicle to a qualified repair shop.

Fuel Gage Inaccurate or Inoperative
Circuit/System Description
The fuel level sender changes resistance based on the fuel level. The engine control module (ECM) monitors the signal circuit of the fuel level sender to determine fuel level. When the fuel tank is full, the sender resistance is low and the ECM senses a low signal voltage. When the fuel tank is empty, the sender resistance is high and the ECM senses a high signal voltage. The ECM uses the signal circuit of the fuel level sender in order to calculate the remaining fuel level percent in the tank. The ECM sends the fuel level message via the serial data circuit to the body control module (BCM). The BCM sends the fuel level percent to the instrument panel cluster (IPC) via the serial data circuit for display on the fuel gage.

Circuit
Short to Ground
High Resistance
Open
Short to Voltage
Signal Performance
Fuel Level Sensor Signal
P0462
1
P0463, P0464
P0463
P0461
Fuel Level Sensor Low Reference
--
1
P0463, P0464
P0463
P0461
1. Fuel Gage Inaccurate or Inoperative

Do you know what a DTC is ? diagnostic trouble code !

P0463 Hyundai - Fuel Level Sensor 'A' Circuit High Input
P0464 Hyundai - Fuel Level Sensor 'A' Circuit Intermittent
P0463 Hyundai - Fuel Level Sensor 'B' Circuit High Input
Possible causes
- Faulty fuel level sensor
- Fuel level sensor harness is open or shorted
- Fuel level sensor circuit poor electrical connection
The fuel level sensor of Hyundai Santa Fe is mounted in the fuel level sensor unit. The sensor detects a fuel level in the fuel tank and transmits a signal to the Engine Control Module (ECM). The fuel level sensor consists of two parts, one is mechanical float and the other side is variable resistor. The fuel level sensor output voltage changes depending on the movement of the fuel mechanical float.

bank 1 sensor 1 lean code. Check vacuum lines first. Could be egr leak also. Most vacuum lines run on the back side of the engine on these. Most common fail is the PCV 90 degree elbow. On the passenger side.

Instead of guessing as to what the problem is or expecting someone on here having a magical fix , take it to a qualified repair shop. Before assuming the worst an wanting to condem the PCM - powertrain control module . Will a scan tool communicate with it ? If your pulling codes it is .
DTC P0603 Control Module Long Term Memory Reset
The PCM has a memory area where it stores certain data it needs to save when the key is turned OFF. This area is called Keep Alive Memory. This diagnostic test monitors the PCM's keep alive memory for a loss or unintended change of data. If such a condition occurs, DTC P0603 will set.
Diagnostic Aids
If the battery has been disconnected for any reason DTC P0603 will set. The PCM keeps a running check on the memory; if memory changes it resets. An intermittent loss of power or ground to the PCM will cause a reset.

Have you disconnected the battery ?
Diagnostic Aids
If the battery has been disconnected for any reason DTC P0603 will set. The PCM keeps a running check on the memory; if memory changes it resets. An intermittent loss of power or ground to the PCM will cause a reset.

P0463 - Fuel Level Sensor Circuit High Input
An excessively high voltage is sent from the sensor is sent to ECM.

The fuel level sensor is mounted in the fuel level sensor unit. The sensor detects a fuel level in the fuel tank and transmits a signal to the ECM or PCM.

It consists of two parts, one is mechanical float and the other side is variable resistor. Fuel level sensor output voltage changes depending on the movement of the fuel mechanical float.


Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)

Possible causes
- Fuel level sersor circuit harness or connectors is open or shorted
- Fuel level sensor may be faulty

Possible solution
Replaced fuel level sensor.

Hope helps (remember to rate this answer).

Pull out your spark plugs. Change them if dirty. There might be a problem with the fuel trim, thats causing spark plug to foul up prematurely. A stucked open EGR valve can also cause a multiple mispfire code(P0300) but then it would be accompanied by an EGR code(P402) which means excessive flow detected. Anyways if was indeed a fouled up spark plug change them as well as the air filter.

THESE ARE FROM THE GM CODE DIFINITION MANUAL, U NEED TO TAKE THIS TO THE DELAER, U HAVE SOME SERIOUS PROBLEMS TO GIVE THIS MANY CODES.

P0300 - Engine Random Misfire Detected
P0441 - Evaporative Emission Control System Incorrect Purge Flow
P0705 - Trans Range Switch Circuit
P1106 - Manifold Absolute Pressure (MAP) Sensor Circuit Intermittent High Voltage
P1133 - Heated Oxygen Sensor (HO2S) Insufficient Switching Bank 1 Sensor 1
P1441 - Evaporative Emission (EVAP) System Flow During Non-Purge
P1662 - Cruise Lamp Control Circuit
P1672 - Low Engine Oil Level Lamp Control Circuit
P1870 - Transmission Component Slipping

Tune it up and replace the 02 sensor that keeps setting the codes bank 2 sensor 1. Have your oil and filter changed right before you go for a retest to. That will clear up 3 codes P0300, 0155 and 0154. You might have to replace the fuel sending unit to get rid of P0463 but if the gauge works OK I'd leave it alone.