Turbocharger Electric Actuator Stepper Motor Fault Codes – Part 2
Had a fault code thrown by the ECU for the Turbocharger Electronic Actuator Stepper Motor or similar?
First up, it’s worth clearing the code to see if the code comes back again. Sometimes it may be just a one-off ‘glitch’ in the ECU.
But if the Turbocharger Electric Actuator Stepper Motor Fault Code persists, read on below…
What are the Common Stepper Motors Fault Codes?
P0234: generic OBD-II code.
This code is usually triggered when the control module for the power train detects over-boost from the turbocharger. The ECU throws this code when after a set period in seconds, a set maximum pressure is detected or exceeded.
Causes of the P0234 Fault Code:
- There is a problem with ‘dumping’ excess pressure due to damaged or clogged vanes or assembly or wastegate.
- There is an issue with the vacuum lines, vacuum control valve or actuator bulb.
- The electric actuator is incorrectly positioning the vanes for the specified boost level.
- The electric actuator is intermittently sticking at a certain point, preventing excess pressure dumps.
Symptoms of the P0234 Fault Code include:
- Over-boost detection triggers ECU to place vehicle into limp mode to protect the engine and power train.
- Gaskets or hose clamps are breached or blown off, creating a whistling noise through gasket breaches, or complete loss of power, due to hoses coming loose.
Diagnosis of the P0234 Fault Code
Make sure correct voltage is being sent to the pressure sensor. And check that the Turbocharger Electric Actuator Stepper Motor can operate across a full range of movement.
Do the stepper motor check first with the actuator arm attached, and then with it detached from the vane-actuating lever. Then check the lever itself, for full and easy range of movement of the vanes inside the turbine housing.
Make sure the boost solenoid is operating correctly, and that there are no split or leaking vacuum hoses.
And if none of the above problems are present, a replacement Electric Actuator Stepper Motor or pneumatic actuator may fix the issue.
But once the issue is deemed as resolved, clear the ECU fault code and retest to affirm problem resolution.
P1251 Stepper Motor Intermittent Fault Code.
The P1251 fault code is the most common code we hear of, when we are dealing with Toyota turbochargers. It is thrown by the ECU in response to over-boosting in the turbocharger. This code usually occurs at times of less engine stress, when you would not expect an over-boost spike.
Causes of the P1251 Fault Code:
- Over-boosting due to vehicle performance mods such as injector upgrades, big bore exhaust, piggybacked ECU. (NOTE: a remapped ECU should not cause this).
- Turbocharger Electric Actuator Stepper Motor is faulty.
- Vanes and/or VNT assembly inside the turbine housing are seized, often due to excess ‘coking’ from incorrect engine combustion.
Note that seized or sticking vanes, can sometimes trigger damage in the stepper motor. The stepper motor’s gearing suffers excessive wear and damage, as it pushes against the VNT actuating lever (due to resistance in the VNT assembly).
Symptoms of the P1251 Fault Code include:
- ECU throwing the P1251 fault code after forcing the vehicle into ‘limp mode’ to protect the engine, power train and sub assemblies from damage.
- Un-even acceleration, especially when the engine is under lighter loads.
Diagnosis of the P1251 Fault Code
We recommend checking the free movement of the vanes and VNT assembly inside the turbine housing. To do so, remove the c-clip from the actuator arm connection. Now move the VNT Lever with the tip of your finger. There should be free and easy movement across the entire arc.
If there isn’t, likely the turbo will need to be disassembled and cleaned or have the VNT assembly rebuilt. A cheaper option available now, is to replace with one of our brand new turbocharger units. This is usually the most cost effective way to go, and you benefit from our exclusive 2 year warranty, as opposed to the usual 3 or 6 months from a used or rebuilt Turbocharger.
If the lever moves freely, then we recommend purchase of a replacement Electronic Stepper Motor, which in the case of the Toyota Hilux, solves the issue around 90% of the time.
And once the issue is deemed as resolved, clear the ECU fault code and retest to affirm problem resolution.
We stock a range or both Turbochargers with or without Actuators, and Stepper Motor Actuators at extremely affordable prices, all with our exclusive 24 month warranty.
And if you have any other query on matching turbo parts for your vehicle, please feel free to contact our sales support on: 0490 059 316.