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Tips and tricks of Chrysler signal relationships

Sunday, July 31, 2011 - 23:00
scope & scan Chrysler signals CMP CKP Chrysler CMP/CKP vehicle diagnostics repair shop training technician training automotive aftermarket

In this month’s column, we will be covering tips, tricks and difficulties of some Chrysler V6 Crankshaft (CKP) and Camshaft (CMP) position sensor pattern relationships. Chrysler has used several different ECMs and PCMs on its 3.8L, 3.5L, 3.2L and 2.7L V6 distributorless ignition engines. Depending on the ECM or PCM design, the crankshaft and cam shaft position sensor signal patterns will be different. Worse yet, different body styles using the same engines changed the CKP/CMP patterns and controllers in different years.

The 3.5L started production in 1993 with the SBEC2 and later the SBEC3 ECM. The 1993 to 1997 3.5L CKP/CMP patterns are the same. From 1998 to 2001, the 3.5L CKP/CMP patterns changed with the use of the SBEC3A, SBEC3A+ ECMs. In 2002, 3.5L Chrysler began using the NGC PCM controller, which again changed the sensor reluctor patterns.

On some body styles — like the JR body — the SBEC to NGS change was made mid-production year. This 2.7L V6 was seen first in 1998. In early production 2004, this engine switched from SBEC3A+ to the NGC controller pattern. So for the 2004 MY, you can have two different sets of CKP/CMP patterns from the installed reluctors on JR body vehicles. If you install an SBEC engine in a NGC controller vehicle, or vise-versa, the engine will not start. You then must change the flywheel and cam gears to the proper ones before the ECM or PCM will allow the engine to run.

On the LH body cars (Intrepid, Concorde and 300M), the 2.7L SBEC was used until 2001 and switched to NGC for 2002. It is safe to swap this 2.7L with the same model year engine from the same body designation, but not a different body designation!

On RS body vehicles with a 3.3L engine, the CKP/CMP pattern was the older SBECB pattern until 2004, when it switched to the NGC controller. The 3.3L never used the later SBEC pattern.

There are three CKP/CMP patterns in use on Chrysler distributorless ignition V6 engines: an early SBEC, a late SBEC and an NGC pattern. SBEC ECMs have two 40-pin harness connectors mounted to a narrow end of the box. NGC PCMs have four 38-pin connectors across wide middle of the box. If you are lucky enough to see the vehicle a replacement engine came out of, this differentiates between SBEC and NGC but not between early or late SBEC controllers. To be sure you are installing the correct engine or parts, look at the flywheel mounted CKP sensor reluctor wheel pattern and the camshaft gear CMP sensor reluctor pattern using either a scope or visual inspection.

The early SBEC pattern is shown in Figure 1. As you can see, the CKP pattern is six evenly spaced groups of four tics for 720 degrees of rotation or one engine cycle. The CMP pattern is 1-2-3-1-2-missing.

The later SBEC pattern is shown in Figure 2. As you can see, this pattern is slightly different than the previous one and easy to miss during assembly. The CKP pattern is in six groups for one engine cycle, but the pattern is 4-4-5-4-4-5. The CMP pattern is close but not the same as the early and runs 1-2-3-1-3-2.

The NGC controller shown in Figure 3 has a CKP pattern that is quite different from the SBEC patterns. This pattern is groups of alternating 15 tics and 16 tics separated by wide pulses that alternate both high and low. The CMP pattern is close but different than both the SBEC patterns. The NGC CMP pattern is 1-2-3-2-1-3.

If you have a no start condition on a Chrysler V6 where you have just a few injector pulses and then none, disconnect the CMP sensor. Many of these V6s will run without a CMP signal. If the engine then starts, either the timing components are out of time, the CMP signal is corrupt or the wrong parts are installed.

Another tip is many LH, JR, JA and JX body cars will begin flashing the green Cruise Control light during an extended cranking no start. If the light flashes, the timing signals are out of time, even if the scan tool CKP/CMP data PID reads "In Sync." I've found, the CKP/CMP data PID will only tell you if there is something wrong and it reads "Out of Sync."

Never turn the flywheel opposite its normal direction of rotation when removing flywheel bolts. There have been many 2.7L and 3.5L that jumped time by allowing the slack in the chain to be on the wrong side of the tensioner. A slightly out of time engine can have unexpected results like a no start for no mechanical reason, just a signal/software one.

Jim Garrido of "Have Scanner Will Travel" is an on-site mobile diagnostics expert for hire. Jim services independent repair shops in central North Carolina. He also teaches diagnostic classes regionally for CARQUEST Technical Institute.

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