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P1251 Toyota Fault Code
P1251 Toyota fault code is somewhat common on modified Toyota Hilux. The fault code itself is due to the turbo over-boosting in the lower load points. Its described as ‘failed stepper motor’ but its commonly not the case. read on to learn more…
How the ECU works and causes P1251 Toyota fault codes
In the lower load levels, the ECU does not ‘close loop boost control’. Basically the ECU has a predetermined ‘VNT position’ table based on the loads. This dictates ‘roughly’ the boost levels, and given the low loads, close enough is seen as good enough. When the load levels come up, the ECU gets into its closed loop, and therefore will do what ever is required to maintain its ‘target boost levels’.
What Causes the P1251 Toyota Fault Code
Basically anything that causes the engine to produce more boost than it should. some examples are:
- High flow exhaust added
This is one of the most common 4wd upgrades done and therefore one of the higher contributors to these issues.
- Piggy back chip
As a piggy back chip is designed to ‘trick’ the ecu, there ends up being more fuel than the ECU knows about and thus creates more exhaust gasses which in turn ‘overspool’ the turbo.
*this is NOT the case for remap!
- Higher flowing injectors / nozzles
For the same reason above!
- Failed Stepper motor
due to the failing stepper motor, it actually holds the VNT in the incorrect position and causes the issue.
- Failed Turbo
Least commonly of all, the actual VNT assembly itself has failed or become physically seized within the engine.
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