LOST JEEPS :: View topic - Crank no start P0725 engine speed sensor circuit

Thank you. Do you know how many volts the sensor puts out? I downloaded a phone oscilloscope app that works with a raspberry pi, but it only works up to 3.3 volts. It did not generate a wave when I tested either sensor, I don't know how set the parameters yet, but the old sensor was putting out around 0.8 volts and the new one was around 2.2 volts when I waved metal at them. The jeep does start now with the new sensor, I just want to make sure before I button everything up.

OPERATION
The crankshaft position sensor is a magnetic pickup type sensor that generates an A/C signal. The sensor contains
a permanent magnet and a coil of wire. The sensor generates an A/C signal each time a notch in the reluctor wheel
on the crankshaft passes across the permanent magnet. The ECM calculates engine speed based on the frequency
of the A/C signal.
If the PCM does not receive a crankshaft position sensor signal within 3 seconds of cranking the engine, it will shut down the fuel injection system.

Author:	jvecchione [ Fri Jul 08, 2022 1:32 pm ]
Post subject:	Crank no start P0725 engine speed sensor circuit
Hello, I have a crank no start condition and suspecting the cps. When I try to start it there is no rpm reading on the tach or my scanner. Fuel pressure climbs to about 18000 kpa and then slowly goes down after I stop. I installed a lift pump last summer and timing belt/water pump over the winter with 0 problems since then. The day it quit was a hot one. Is there anything else I can try to diagnose this? It looks like if I move the coolant overflow out of the way I can maybe get to the cps? Sent from my SM-A326U1 using Tapatalk

Author:	WWDiesel [ Fri Jul 08, 2022 2:41 pm ]
Post subject:	Re: Crank no start P0725 engine speed sensor circuit
jvecchione wrote: Is there anything else I can try to diagnose this? Short of having an oscilloscope to test the CPS signal and if you did not get any DTC's when using a scanner, no. The CPS are known for going bad and not producing a signal as they go through the heat up cycle of the engine. Some have put a ohm meter on the signal pins and put the CPS in a pot of water and heat the water on a stove and monitor the signal to see if it looses continuity as it goes thought a heat up cycle. They don't always set a DTC when they go bad either, so you cannot depend on that as a true indicator. When mine was going bad back many years ago, it put me on the side of the road twice and never set any DTCs. I had to set there until it cooled off and allowed the engine to restart. Best to just replace it, and it is much easier to access it from underneath the vehicle if you can get on a lift or drive up ramps. If you have to jack it up, be SURE and use jack stands and do it safely. See picture 2 below. Autozone can provide you with the OEM Bosch CPS in their "reboxed" Duralast line; that is where I purchased mine about 10 years ago. Duralast Crankshaft Position Sensor Part #SU8492

Author:	jvecchione [ Thu Jul 14, 2022 10:32 am ]
Post subject:	Re: Crank no start P0725 engine speed sensor circuit
Thank you. Do you know how many volts the sensor puts out? I downloaded a phone oscilloscope app that works with a raspberry pi, but it only works up to 3.3 volts. It did not generate a wave when I tested either sensor, I don't know how set the parameters yet, but the old sensor was putting out around 0.8 volts and the new one was around 2.2 volts when I waved metal at them. The jeep does start now with the new sensor, I just want to make sure before I button everything up. Sent from my SM-A326U1 using Tapatalk

Author:	WWDiesel [ Thu Jul 14, 2022 1:55 pm ]
Post subject:	Re: Crank no start P0725 engine speed sensor circuit
jvecchione wrote: Thank you. Do you know how many volts the sensor puts out? I downloaded a phone oscilloscope app that works with a raspberry pi, but it only works up to 3.3 volts. It did not generate a wave when I tested either sensor, I don't know how set the parameters yet, but the old sensor was putting out around 0.8 volts and the new one was around 2.2 volts when I waved metal at them. The jeep does start now with the new sensor, I just want to make sure before I button everything up. According to the FSM, the CPS is just a two wire magnetic pickup positioned close to a toothed reluctor wheel on the crankshaft. The FSM does not show the voltage used by the FSM across the sensor. Some sensors use 5v reference voltage provided by the ECM. Quote: OPERATION The crankshaft position sensor is a magnetic pickup type sensor that generates an A/C signal. The sensor contains a permanent magnet and a coil of wire. The sensor generates an A/C signal each time a notch in the reluctor wheel on the crankshaft passes across the permanent magnet. The ECM calculates engine speed based on the frequency of the A/C signal. If the PCM does not receive a crankshaft position sensor signal within 3 seconds of cranking the engine, it will shut down the fuel injection system.

Author:	CATCRD [ Sun Jul 24, 2022 8:21 am ]
Post subject:	Re: Crank no start P0725 engine speed sensor circuit
I don't know if you already found the problem, but just to document it here, my other CRD threw a P0725 and P0700 last month. No other symptoms. I had replaced the crank sensor 10 years ago after the engine started randomly quitting when hot, with no codes. That solved it until now. Replaced it again with the Duralast part, cleared the codes and all has been well for a month or so.

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