What this code means
P0201 may mean the engine control module is seeing a possible problem with the cylinder 1 fuel injector control circuit.
What the vehicle may do
- The vehicle may run rough or feel like it has a misfire.
- A warning message may appear, especially if an emissions-related message is involved.
- Performance may be reduced depending on how the fault is detected.
Possible fault areas
- Possible wiring, terminal, or connector concerns in the cylinder 1 injector circuit.
- Possible fuel injector electrical fault.
- Possible engine control module driver or control-side concern.
Diagnostic path
Opening and diagnostic frame
On this Silverado 2500 with the 6.6 diesel, P0201 may point to a problem in the cylinder 1 fuel injector control circuit. The truck may run rough, show a misfire, lose some performance, or bring up service emissions or exhaust fluid messages. The broad fault areas are possible wiring or terminal problems at the injector circuit, a possible cylinder 1 injector issue, or a possible engine control module driver issue. Start with the basic system checks, then follow a structured diagnostic approach instead of jumping straight to a part.
Understand when the monitor is valid
Before testing, know what the circuit is trying to do. The voltage supply output circuit is switched to 50 V to activate the injector. The monitor runs with battery voltage greater than 11 V, the engine running, and then runs continuously after those gates are met. The fault logic is command versus actual state: if the commanded state does not match the actual state for greater than 1 s, the code can set. For cylinder 1, also remember that cylinder 1 and cylinder 4 are in the same injector group, so group-related codes can change which electrical path you take.
Initial verification before circuit testing
With ignition on, vehicle in service mode, use this verification for the fuel injector component code. First sort the scan results. If injector group supply codes are present, or if other codes are present, do not ignore them; use that information to pick the correct branch. If no code is currently set, run the engine and watch the Cylinder 1–8 Current Misfire Counter. Wiggle the K20 Engine Control Module harness and connectors while watching that counter. The counter should not increment. If it increments during the wiggle test, repair the wiring, terminals, or connector concern as necessary. If it does not increment, operate the vehicle within the monitor gates, or under the captured conditions, and confirm P0201 does not reset. If it does reset, pause, recheck the earlier diagnostic path, and avoid guessing.
Cylinder 1 circuit path when the target injector code is the driver
For the cylinder 1 injector circuit testing, work with ignition off first and disconnect electrical connector X2 at the K20 Engine Control Module. Use the correct terminal information: voltage control is control circuit terminal 1, and voltage supply is control circuit terminal 2. Test the voltage supply control circuit to ground. It should show infinite resistance. If it does not, disconnect the cylinder 1 injector connector and test the voltage supply circuit at the control module harness to ground again. If it is still less than infinite resistance, repair the short to ground on that circuit. If it becomes infinite resistance, test the voltage control circuit at the control module harness to ground. If that circuit is less than infinite resistance, repair the short to ground. If it is infinite resistance, the path moves to testing or replacing the fuel injector.
Short-to-voltage and continuity checks for that path
If the voltage supply-to-ground resistance is infinite, turn ignition on in service mode and test voltage supply at the control module harness to ground. The expected result is less than 1 V. If it is 1 V or greater, disconnect the cylinder 1 injector and test that same point again for less than 1 V. If it stays 1 V or greater, repair the short to voltage on the voltage supply circuit. If it drops below 1 V, repair the short to voltage on the voltage control circuit. If the first voltage check is already less than 1 V, turn ignition off and test between voltage supply and voltage control at the control module harness. The expected result is less than 3 Ω. If it is 3 Ω or greater, disconnect the injector and check both circuits end to end from the control module harness to the component harness. Each circuit should be less than 2 Ω. If either one is 2 Ω or greater, repair the open or high resistance in that circuit. If both are less than 2 Ω, the path moves to testing or replacing the injector. If the supply-to-control resistance at the control module harness is less than 3 Ω, replace the K20 Engine Control Module.
When injector group supply codes are present with P0201
If injector group supply codes are present along with the target injector circuit code, the electrical path starts the same way: ignition off, disconnect X2 at the K20 Engine Control Module, and test voltage supply to ground for infinite resistance. If it is less than infinite resistance, disconnect the cylinder 1 injector and isolate whether the short to ground is on the voltage supply circuit or the voltage control circuit, then repair the circuit indicated by the test. If the ground check passes, turn ignition on in service mode and check voltage supply at the control module harness to ground for less than 1 V. If it is 1 V or greater, disconnect the injector and use the follow-up voltage check to decide whether the short to voltage is on voltage supply or voltage control, then repair that circuit. If the voltage check is less than 1 V, turn ignition off, disconnect the injector, and check both control circuits end to end. Each should be less than 2 Ω. If either is 2 Ω or greater, repair the open or high resistance. If both pass, test between control circuit terminal 1 and terminal 2 at the component harness. That should be infinite resistance. If it is less than infinite resistance, repair the short between the circuits. If it is infinite resistance, move into component testing. If component testing fails, replace the fuel injector. If component testing passes, replace the K20 Engine Control Module.
When the group supply code is present by itself
If the injector group supply code is present but no other codes are set, the path is shorter. Start with ignition off. Disconnect X2 at the K20 Engine Control Module, then disconnect the cylinder 1 fuel injector connector. At the component harness, test between control circuit terminal 1 and control circuit terminal 2. That circuit-to-circuit check should be infinite resistance. If it is less than infinite resistance, repair the short between the circuits. If it is infinite resistance, move into component testing. If component testing fails, replace the fuel injector. If component testing passes, replace the K20 Engine Control Module.
Fuel injector component test
For component testing, keep ignition off and disconnect the cylinder 1 injector connector. The specified resistances are valid for components at room temperature. Test between control terminal 1 and control terminal 2. The injector should measure between 0.2 and 1.5 Ω. If it is not in that range, replace the fuel injector. If it is in range, test from each injector terminal to the injector housing. Each terminal-to-housing test should show infinite resistance. If either one is less than infinite resistance, replace the fuel injector. If both are infinite resistance, the component test is OK.
Repair verification and close
Keep verification separate from the circuit testing. After the repair is complete, verify the repair and confirm the code stays gone. Also check the scan tool event data under the exhaust gas recirculation system malfunction warning event data; those parameters should display No. If any parameter displays Yes, operate the vehicle within the monitor gates for the DTC identified by that event data. A driver message or speed limitation may not clear until the DTC that caused it runs and passes, so driving may be required. Takeaway: do not condemn the injector until the cylinder 1 control and supply circuits prove clean; then let the component test and final verification make the call. For more diagnostic training, visit stepdiagnostics.com.
Final check
P0201 is often approached as an electrical command-versus-response diagnosis, so the circuit checks and component test should guide the repair decision.
For more guided automotive diagnostics, visit STEP Diagnostics.
