Hong Kong Rainbow Diagnostics | 2012 Honda Crosstour Cold acceleration abnormalities
Failure phenomenon
This is a 2012 Honda Crosstour with K24Y3 engine and about 362,000 kilometers. The vehicle idles and refuels in place without any abnormality, but there is a noticeable stutter when starting from cold and accelerating.After replacing the MAP sensors, MAF sensors, crankshaft/camshaft position sensors, spark plugs, ignition coils, and injectors at his factory, and calibrating them several times, he still could not solve the problem, so he commissioned technical support.
Fault Diagnostics
No DTC error codes were found using the diagnostic computer. The road test monitoring data stream (Figure 1) shows a large fluctuation in RPM synchronized with the MAP measurement at the time of the failure.
Fig. 1 Streaming of engine data at the time of failure
The CKP signal was measured with an Acer Pico oscilloscope (Fig. 2), and the RPM showed a regular oscillation, similar to idling "spinning".
However, no fire was observed. The idle real-time waveform (Fig. 3) shows that the VTC control valve duty cycle is about 31 TP3T.This means that the variable valve timing is not intervening.
Fig. 2 Crankshaft Position Sensor Signal Waveforms during Fault Occurrence
Fig. 3 Engine Timing Waveforms at Idle State
The VTC controls the duty cycle when a fault is indicated by a repeated road test. Rapidly pulling up from ~18% to ~45% (Figure 4).Synchronization causes fluctuations in RPM and MAP signals, presumably due to abnormal VTC control.
Fig. 4 Signal Waveforms of Fault Status
反覆路試顯示故障時 VTC 控制占空比由約 18% 快速拉升至約 45%（圖4），同步造成轉速與 MAP 訊號波動，推測症狀源自 VTC 控制異常。 放大占空比 18% 時波形（圖5）可見 CMP 訊號相較怠速提前約 6 齒（1 齒＝6° 曲軸角）The crankshaft angle is advanced by about 36°, which is recognized as abnormal.
Fig. 5 Amplified waveform of VTC solenoid control signal with duty cycle of about 18%.
At duty cycle 45% (Fig. 6), the CMP signal position is back to the idle speed reference, which is also unreasonable.
Fig. 6 Amplified waveform of VTC solenoid control signal with duty cycle of about 45%.
Synthesis: Inconsistency between the PCM control logic and the actual camshaft position feedback causes the PCM to frequently correct the VTC, which in turn leads to stuttering during acceleration. Possible causes include:VTC solenoid valve failure, insufficient oil pressure, VTC actuator failure
fault resolution
Following the principle of "from easiest to hardest". Replace with original VTC solenoid valve first.After several road tests, the symptoms were completely eliminated. One week after the return visit, it was confirmed to be working normally and no recurrence.
Fault Summary
This is a case of 2012 Honda Crosstour with abnormal cold acceleration.It was ultimately determined that this was not due to an abnormal control of the factory VTC solenoid valve.
ThroughHonghong pico automotive oscilloscopeThe engineers were able to grasp the actual changes in the CKP/CMP and VTC control signals, accurately determine the camshaft phase shift, and quickly pinpoint the root cause of the problem, which led to a no-disassembly diagnosis and complete troubleshooting.The professional value of data-driven maintenance and accurate diagnosis.
