CAT 33 Fault Code: Turbo Wastegate Solenoid current low
Also called Turbo Wastegate Solenoid current hig, Turbo Wastegate Solenoid current high, Turbo Wastegate Solenoid current mismatch
Turbo Wastegate Solenoid current low · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
CAT code 33 (SPN 646 / FMI 5) covers turbo wastegate solenoid current problems on C15 and C18 engines: low current (open circuit), high current (short circuit), or a current mismatch where actual boost does not match desired boost. The ECM controls the wastegate solenoid to regulate turbo boost pressure, so this code points to wiring, solenoid, or airflow restriction issues affecting that control loop.
Medium severity. The engine will typically keep running, but boost control is compromised, which can mean reduced power, poor fuel economy, or turbo stress if left unaddressed. Diagnose within the shift rather than ignoring it.
What does CAT error code 33 mean?
This code relates to the turbocharger wastegate solenoid, a component the ECM uses to control how much exhaust gas bypasses the turbine wheel. By adjusting the wastegate position, the ECM controls turbocharger speed and boost pressure delivered to the intake manifold.
There are three distinct fault conditions bundled under code 33: a low current (open circuit) condition, a high current (short circuit) condition, and a current mismatch condition where actual boost pressure falls short of desired boost while solenoid current is near maximum. Each points to a different part of the control circuit or airflow path failing to do its job.
In all three cases, the ECM cannot properly regulate boost, which affects engine power, turbo response, and potentially fuel efficiency. It is not usually an immediate stop-the-engine emergency, but it should not be ignored for long.
What triggers a CAT 33 code?
For the low current (open circuit) condition: the ECM detects low current in the wastegate solenoid circuit for more than 0.12 seconds, with battery voltage above 9 V and desired current more than 0.2 amp. For the high current (short circuit) condition: the same 0.12 seconds duration, 9 V battery voltage floor, and 0.2 amp desired current threshold apply, but with a high current condition instead. For the current mismatch condition: actual boost is less than desired boost by more than 30 kPa (4.4 psi) for more than eight seconds, the turbocharger solenoid current is greater than 80% of its maximum value, desired boost is not zero, and the ECM has been powered for at least two seconds.
Common causes of 33
- ECM connection problems, including corroded or loose connectors at the ECM
- Failure of the wastegate control solenoid itself (the solenoid alone can often be replaced instead of the entire valve assembly)
- Damaged or broken harness between the ECM and the wastegate control solenoid
- ECM failure
- Air inlet system restrictions or exhaust system restrictions that affect airflow to the wastegate
- A plugged drain orifice in the wastegate control circuit
- Debris in the system causing wastegate solenoid failure
- Air not reaching the wastegate solenoid
- A blocked bleed orifice, which prevents the wastegate from closing properly when the solenoid is closed
- Wastegate solenoid O-ring failure
- Wastegate failure itself, separate from the solenoid
How to troubleshoot CAT 33: first checks
- Inspect the ECM connector and the wastegate solenoid connector for corrosion, loose pins, or damage
- Check continuity and condition of the harness running between the ECM and the wastegate control solenoid
- Visually inspect the wastegate solenoid for physical damage and test its resistance/current draw against expected values if you have the ECM service tool available
- Look for air inlet or exhaust restrictions that could be preventing proper airflow to or from the wastegate system
- Check the drain orifice and bleed orifice in the wastegate air circuit for blockage or debris
- Inspect the wastegate solenoid O-ring for wear or failure that could allow air leakage
- Confirm battery voltage is stable and above the 9 V floor the ECM needs to evaluate this circuit accurately
How the code clears
No separate clearing step is listed. Once the underlying wiring, connector, solenoid, orifice, or airflow restriction issue is repaired, the code should stop being active on the next key cycle or diagnostic check, but confirm with a scan tool that the fault is no longer present after repairs.
Affected models and serial ranges
33 appears in our records across 2 CAT models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| C15 | Serial range not listed in source records |
| C18 | Serial range not listed in source records |
Frequently asked questions
What does CAT fault code 33 mean?
It means the ECM has detected a problem with the turbo wastegate solenoid circuit, either a low current (open circuit) condition, a high current (short circuit) condition, or a mismatch between desired and actual boost pressure tied to solenoid current. It maps to SPN 646 / FMI 5 and applies to C15 and C18 engines.
Can I keep driving or operating with code 33 active?
The engine will generally keep running, but boost control will be off, which can mean noticeably reduced power or poor response under load. It is best treated as a diagnose-soon issue rather than something to run indefinitely.
What parts commonly cause this fault?
The wastegate control solenoid itself is a frequent cause, and it can often be replaced separately instead of swapping the entire wastegate valve. Wiring and connector issues between the ECM and solenoid, blocked orifices, air restrictions, and O-ring failure on the solenoid are also listed causes.
Is this a wiring problem or a mechanical problem?
It can be either. The low current and high current variants point more toward wiring, connectors, or the solenoid coil itself. The current mismatch variant points more toward mechanical issues like blocked orifices, debris, airflow restriction, or wastegate failure, even though solenoid current is still part of what triggers it.
Does a plugged drain or bleed orifice really cause this code?
Yes. The wastegate system relies on air being routed to the wastegate and then bled off through an orifice so the wastegate can close properly. If that orifice is blocked, the wastegate cannot respond correctly, which can trigger the current mismatch version of this code.
What voltage does the ECM need to detect this fault accurately?
Battery voltage needs to be above 9 V for the ECM to evaluate the low current and high current conditions on this circuit.
How is the boost mismatch version of this code different from the current version?
The mismatch version triggers when actual boost is below desired boost by more than 30 kPa (4.4 psi) for more than eight seconds, while wastegate solenoid current is above 80% of maximum, desired boost is not zero, and the ECM has been powered at least two seconds. This is a performance-based trigger rather than a simple circuit current fault.