Crank And Cam Position Sensor Good Trouble Shooting Help Info
Found This on The Web, don't know if it has been share before, .. Very good explanation Voltage variation on some system that could cause voltage drop and cause the crank position sensor not to output the back the PCM.. = won't start or died.. the way i read it especially on Prior to 1996"
Voltage Reference. Prior to 1996, Chrysler PCMs shared the 5-volt reference among all inputs, which can cause some unusual no-start conditions.: "
Solving the mysteries of Chrysler ignitions
Although not radically different from other designs, Chrysler's newer ignition systems can throw you one nasty diagnostic curve if you're not up on some of their idiosyncrasies.
Chrysler ignition systems are different enough from others out there to seem almost mysterious to the average tech working in a multibrand shop. Because of this, some common failures tend to result in lots of wasted diagnostic time. This article will focus on the design of Chrysler's newer systems and give you tips on how to solve some common problems. Before we begin, note that a late-model Chrysler could have one of three types of ignition systems-DI (conventional distributor), El (no distributor, with coil packs) or EI-COP (no distributor, with individual coils).
All of these systems have some commonality. For instance, Chrysler uses a transmission-mounted crankshaft position sensor (CKP) for the ignition trigger signal as well as misfire detection. A part called an ASD Relay provides power for the coil and other essential circuits. This relay is activated only for a couple of seconds when the key is first turned on and remains on as long as the PCM receives a crank signal. On all domestic production Chrysler engines, the ignition primary circuit is switched by the PCM directly; there is no "module."
The location of the cam position sensor (CMP) varies with the type of engine and ignition system. On DI systems, the cam sensor is integrated into the distributor; on other applications, it's on the front of the engine and reads off the cam sprocket.
The PCM sends approximately 5 volts to a Hall effect sensor, which is required to operate the Hall effect chip and the electronics inside the cam sensor. The ground for the sensor is provided through its return circuit.
The input to the PCM occurs on a 5-volt output reference circuit. The CMP sensor operates in the same manner as the CKP sensor, except that with the CMP sensor, there are only two edges to detect. The PCM identifies camshaft position by registering the change from 5 to 0 volts or 0 to 5 volts, as signaled by the cam sensor.
In Chrysler's coil-on-plug ignitions, there's one coil for each cylinder, and it's attached to the engine directly above the spark plug. A rubber boot contains a stainless-steel spring, which serves as the secondary conductor between the coil and the plug.
The coils are powered by the ASD Relay when the key is first turned on and the PCM is receiving a crank signal. The ground side is switched by the PCM. There's also a capacitor on each bank of the engine for RFI suppression. Note that each coil fires only once per ignition event, unlike DIS waste-spark systems, which fire twice.
The PCM grounds the proper coil based on signals from the CKP and CMP sensors. When spark is required, the PCM opens the ground circuit, causing the coil's magnetic field to collapse and generate high secondary voltage. The PCM also monitors the primary circuit of each coil and will set a DTC if there's a circuit fault.
Misfire is detected by analyzing crankshaft speed fluctuations. The crank sensor detects engine speed, and an rpm value is established for each cylinder for comparison. When a sufficient difference in rpm occurs among cylinders, a misfire count is recorded. The rpm varies slightly because of different input variables.
Two types of misfires can be detected. A two-trip misfire, which occurs about 2% of the time, will result in an emissions increase. A one-trip misfire, also called a catalyst-damaging misfire, occurs in about 10% to 20% of the events.
To detect a misfire, the PCM must first learn the spacing of the crank target windows. This is done when the engine is in the Deceleration Fuel Shutoff mode. To learn the crank target spacing, three closed-throttle decelerations from 55 mph to rest must be performed. The misfire monitor will not be enabled until this spacing is learned.
The PCM also checks the machining tolerances within each group of slots on the flywheel. The PCM calculates the variation among each group of slots. This calculation is called rpm error. The variation in rpm readings between cylinder pairs must be less than 5% in order to run the misfire monitor.
Once the PCM has detected a misfire for two consecutive trips, the MIL will be continuously illuminated and a permanent DTC will store. If the PCM detects a catalyst-damaging misfire, the MIL will flash. If the active misfire ends, the MIL will change to continuous illumination. The MIL will remain on for more than one trip, but will go out if the conditions that set the DTC are not found on subsequent trips.
Common Problem Areas
The following problems are commonly found on Chrysler ignition systems, but there are ways to solve them:
ASp Relay. When you perform a diagnosis for a no-start condition on a Chrysler vehicle, remember that the ASD Relay will not activate without a crank signal. Many techs waste time trying to figure out why there's no power at the injectors, coils and other components without manually activating the relay. The relay can be activated using a scan tool and Chrysler's Actuator Test Mode (ATM). In fact, a scan tool also can be used to verify the system's ability to produce spark.
Since the ASD Relay powers up numerous circuits, components that don't seem to be related to the ignition system can cause a no-start condition. On some systems, for example, the oxygen sensor heater elements are switched by the ASD Relay. So a shorted 02 sensor can lower the voltage available to the ignition system to the point where the engine won't start. Remember to check the available voltage at the coils) while the ASD Relay is activated and compare it to source voltage.
By the way, Chrysler checks the 02 heater circuits by activating the ASD Relay after the engine is shut down. Note that this relay also supplies power to the fuel pump. It stands to reason, then, that if you're working on the fuel system, you'll want to disconnect the battery before cracking open any lines!
Distributor/CMP. Misfire DTCs, rough running and low power are all possible symptoms of a distributor that's "out-of-sync." The distributor is adjustable on V8 truck applications. The distributor position has no effect on timing, however, since a crank sensor is used. A problem can occur on Chryslers when the distributor cap terminals are not lined up with the rotor tip when the coil fires. If the distance to the terminal connected to the previous or next cylinder in the firing order is short enough, the spark will jump the wrong gap, hence the driveability problems.
Chrysler made it easy to check the synchronization of the distributor to the crankshaft with a scan tool through its Set Sync test. To conduct this test, select Set Sync Mode in the Deluxe CDR screen. A message on the display tells you that the engine is at idle speed and that the transmission is in Park or Neutral. The next screen indicates the distributor setting. If that's not at zero, manually adjust the distributor until it reaches that value.
CMP/CKP Sync. The synchronization of the CMP and CKP sensors could be another source of confusion when diagnosing a no-start condition on El Chryslers. A scan tool can report on the presence of the CMP and CKP signals, and whether they're in sync. For a Chrysler engine to start, the PCM must receive a good signal from both the CKP and CMP sensors. Once the engine is running, the cam signal is no longer needed for operation on vehicles built after 1996.
However, the PCM needs the crank signal to diagnose a potential problem with the cam signal, and vice versa. If the PCM receives an incorrect or incomplete signal from either sensor, it may set an erroneous DTC. The scan tool may also indicate the presence of either signal incorrectly. If either sensor is suspected of malfunctioning, both should be checked with a lab scope. Diagnostic Note: If the CMP and/or CKP sensors are out-of-sync, the Cruise light will flash while the engine is running.
CMP Signal Loss. As I just mentioned, late-model Chrysler engines can continue to run if the CMP signal is lost. If this occurs at idle, the rpm will jump to around 2000. Loss of the cam signal while cranking can cause the Cruise light to come on, as well, and set numerous DTCs for the ignition primary circuits, the crank sensor and the ASD Relay. Excessive coil dwell can even blow fuses.
Note that if the cam sensor is internally shorted, the ASD Relay may activate with the key on and engine off.
Voltage Reference. Prior to 1996, Chrysler PCMs shared the 5-volt reference among all inputs, which can cause some unusual no-start conditions. Here's how the reference voltage is used:
Inside the PCM is a chip that takes system voltage, which varies, and regulates it to a constant 5 volts. This power source is used in a number of ways. For example, in a TP sensor, the reference voltage is applied to one end of a resistor, with the other end connected to ground. All the voltage drops across the resistor, but since it has a high resistance value, the source voltage remains at 5 volts. A wiper is connected to provide the throttle position input voltage to the PCM. As the wiper moves closer to the grounded end of the resistor, the throttle position voltage decreases, and as it moves toward the 5-volt end, it increases.
In the case of a coolant temperature sensor, the voltage is actually pulled to ground by a resistor in the sensor. However, before the ECT reference voltage leaves the PCM, it goes through an internal resistor. Once again, the value is high enough that the source voltage remains at 5 volts. Note that in neither case is the output of the 5-volt regulator shorted to ground before it goes through the resistor.
In the case of switches, including Hall effect devices such as CKP and CMP sensors, the 5-volt reference goes through a resistor to the sensor signal line. The sensor receives power and ground and switches the 5 volts to ground as the engine turns.
I'll bet some of you have made the connection already: If the 5-volt reference is shorted to ground on a sensor that receives power from it-such as a TP, MAP or a/c pressure sensor-there will be no reference to the CMP or CKP sensor.
In this case, if an LED test light or a logic probe is connected to the sensor signal wire and the engine is cranked, the light will blink if the sensor is good! Remember, though, even if the sensor is good, the PCM won't "see" it without the proper reference voltage.
Another indication of a reference voltage problem is a PCM that won't communicate. In 1997 and later systems, Chrysler added additional voltage reference sources so that a noncritical sensor wouldn't cause a motorist to have to walk home.
Keeping the design of this circuit in mind, you can check the harness to the CMP or CKP sensor by looking for power and ground as well as a 5volt reference on the signal wire.
Sensor Adjustment. While you can't change the timing, some of Chrysler's crank sensors are adjustable for clearance with the flywheel. When you get a new sensor, it may come with a paper shim glued to the end. Once the sensor is installed, make sure the shim touches the flywheel before torquing the mounting bolt.
If you have to remove the flywheel for other service work, remove the crank sensor first, to prevent damage. If you're reinstalling the old sensor, you need to stick a new shim (Part No. 5252229) on the end of it to maintain the proper air gap to the flywheel.
The differences between Chrysler ignition systems and those of other makes are not really that radical. After all, most ignition systems work in a similar manner and will allow many general diagnostic techniques to be applied. However, learning the idiosyncrasies of Chrysler ignitions will make you a more successful diagnostician. We hope this article is a good step in that direction.
Last edited by fonzy35; 09-25-2010 at 09:41 PM.