V0122 (126-4) Permanent DTC F-CAN MALFUNCTION (ECM) PCM - VSA CONTROL MODULE UNIT) but no Service Engine light

'year make model' in all question please.

P0203 OBD-II Trouble Code: Injector Circuit Malfunction

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The P0203 is a diagnostic trouble code that is set when the engine control module (ECM) has detected a fault in the injector circuit for cylinder 3. The ECM ...

P0203 Code: Injector Circuit / Open - Cylinder 3 - CarParts.com

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Diagnostic trouble code (DTC) P0203 stands for "Injector Circuit/Open - Cylinder 3." The powertrain control module (PCM) may set this code if it ...
Nov 11, 2021 · Uploaded by The Flat Rate Mechanic

Error Code P0203: Cylinder 3 Injector Circuit Malfunction

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Error Code P0203 is defined as Cylinder 3 Injector Circuit Malfunction. This code means the PCM (powertrain control module, also known as ECM or engine ..

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.

DTC 31 Is a vacuum sensor (MAP) signal/vacuum sensor or circuit,Electronic control module malfunction (ECM,PCM)

When a 'check engine light' (MIL=Malfunction Indicator Lamp) is turned on, there is a DTC (Diagnostic Trouble Code) set/stored in the ECM/PCM (Engine Control Module/Powertrain Control Module). This code identifies which engine management system component/function experienced a malfunction. Once you pull/read this code, you may begin diagnosis.

Check Engine Light? When a 'check engine light' (MIL=Malfunction Indicator Lamp) is turned on, there is a DTC (Diagnostic Trouble Code) set/stored in the ECM/PCM (Engine Control Module/Powertrain Control Module). This code identifies which engine management system component/function experienced a malfunction. Once you pull/read this code, you may begin diagnosis.

Is the "Check Engine" light on? When a 'check engine light' (MIL=Malfunction Indicator Lamp) is turned on, there is a DTC (Diagnostic Trouble Code) set/stored in the ECM/PCM (Engine Control Module/Powertrain Control Module). This code identifies which engine management system component/function experienced a malfunction. Once you pull/read this code, you may begin diagnosis.

When a 'check engine light' (MIL=Malfunction Indicator Lamp) is turned on, there is a DTC (Diagnostic Trouble Code) set/stored in the ECM/PCM (Engine Control Module/Powertrain Control Module). This code identifies which engine management system component/function experienced a malfunction. Once you pull/read this code, you can begin diagnosis.

When a 'check engine light' (MIL=Malfunction Indicator Lamp) is turned on, there is a DTC (Diagnostic Trouble Code) set/stored in the ECM/PCM (Engine Control Module/Powertrain Control Module). This code identifies which engine management system component/function experienced a malfunction. Once you pull/read this code, you may begin diagnosis.

P0203 - Injector Circuit Malfunction Cylinder 3

Powertrain Control Module (PCM) or Electronic Control Module (ECM) checks the injectors circuit resistance and monitors the voltage drop during normal operation. The PCM/ECM will trigger the P0203 code when the resistance or voltage drop at the injector #3 is out of specifications.

Causes:
- Open or shorted wiring harness to the injector #3
- Bad injector #3
- Bad PCM/ECM

Solutions:
- If damage, repair injector wire harness or connector
- Replace injector
- Replace PCM or ECM


P0204 - Injector Circuit Malfunction Cylinder 4

Same info as the P0203 DTC


P0300 - Random/Multiple Cylinder Misfire Detected

When a misfire occurs, engine speed will fluctuate. If the engine speed fluctuates enough to cause the crankshaft position (CKP) sensor (POS) signal to vary, Powertrain Control Module (PCM) or Electronic Control Module (ECM) can determine that a misfire is occurring.

Causes:
- Improper spark plug
- Insufficient compression
- Incorrect fuel pressure
- The injector circuit is open or shorted
- Fuel injectors may be faulty
- Intake air leak
- The ignition signal circuit is open or shorted

Solutions:
- Perform Injector Service
- Replace Spark Plugs
- Replace Injectors
- Replace Ignition Coils

It could be the electronic power steeirng module . With the gauges dropping out like that , the module could be bring down the data bus . Don't know how much you know about automotive electronic's an how the insturment cluster know's what speed to set speedo at an how full fuel gauge is an rpm on the tach .
Speedometer
The instrument panel cluster (IPC) displays the vehicle speed based on the information from the engine control module (ECM)/powertrain control module (PCM). The ECM/PCM calculates the vehicle speed based on the class 2 message indicating the wheel reference speed from the electronic brake control module (EBCM) if:
• The ECM/PCM detects a malfunction in the vehicle speed sensor circuit.
• The IPC detects a loss of class 2 communications with the ECM/PCM.
The speedometer defaults to 0 km/h (0 mph) if the IPC detects a loss of class 2 communications with both the ECM/PCM.

012 GM Class II Communications

Checking the vehicle modules for DTC'S - diagnostic trouble codes is the first place to start .
The Power Steering Control Module (PSCM) receives a class 2 vehicle speed message from the Engine Control Module (ECM) via a class 2 serial data circuit. The PSCM uses this vehicle speed message, and other inputs, to determine the desired amount of steering assist.
DTC C0000
DTC C0475
DTC C0476
DTC C0545
DTC C0847
DTC C0848
DTC C0896
DTC C0899
DTC C0900

your best bet ,take it to a qualified GM repair shop .