Cam Shaft Position Sensor (CMPS) is hall sensor type. Sensing the teeth attach at the end of cam shaft, CMPS detects rotation of Cam shaft. (1 signal per 1 rotation) As Cam shaft rotates once while Crank shaft does twice, CMPS reference point generates once while CKPS' do twice. As this signal inputted to ECM, it distinguishes crank angle and the cylinder which requires fuel injection in order to determine injection sequence and duration.
P0340 is set corresponding to the condition of ECM internal counter when CMPS signal does not generate while CKPS signal is outputted. This code is due to the failure relevant to CMPS related circuit and sensor component.
Item
Detecting Condition
Possible Cause
DTC Strategy
Signal monitoring
CMPS circuit
CMPS
Enable Conditions
During accelerating and turning engine ON
Threshold Value
CKPS signal is outputted while CMPS signal does not generate.
Diagnostic Time
Corresponding to ECM internal counter condition.
Fail Safe
Fuel cut
NO
When CKPS failure, backup mode starts using only CMPS.
When CMPS failure, backup mode starts using only CKPS.
When Both CKPS and CMPS simultaneous failure, engine off
EGR Off
Fuel Limit
Check Lamp
ON
Sensor Type
Output Signal
Characteristic
Air Gab
LOW Signal
Detecting Voltage
HIGH Signal
Hall effect type
0V ~ 5V Digital signal output
0.5 ~1.5 mm
Below 2.0V
Above 3.8V
Fig.1) This shows waveform of CKPS and CMPS simultaneously. The middle area indicates reference points of CKPS and CMPS.
? Injection sequence is determined based on Low and High signal of CMPS reference point as detecting cylinder position.
CMPS signal waveform analysis.
ECM recognizes High signal as Low signal when CMPS signal drops below 2.0V and Low signal as High signal when CMPS signal rises above 3.8V.
V0 - the Minimum voltage of Low signal does not drop below 0.0V due to the hall sensor inside resistance. When the Minimum voltage of Low signal is above 0.6V during signal waveform inspection, check excessive resistance inside of CMPS component or in ground circuit.