Intermittent P0341

[1998RIVMAN]

I have been getting a cam position sensor code on and off for a while. Already had the sensor replaced. Going to troubleshoot wiring and ICM next.
The odd thing, to me, is that I only get what appear to be misses (no misfire codes) at light loads according to a scan. WOT no problems at all..idle no problems at all. Code does not set all of the time. I can't figure it as a missing magnet problem, nor can anyone of the techs at my shop. I was gonna try waving a dead chicken over it next. Has anyone else run into this before? Am I missing something in the operation of this system, in that it only malf. at light load?

Thanks in advance. Im sure that you've seen this before but I can't find similar situation to refer to.

[1Hot97]

Aha, a 341 code:

DTC P0341 CMP Sensor Circuit Performance
Ignition Control Module.

Circuit Description
The camshaft position PCM input is produced by the ignition control module. The
1CM produces the camshaft position PCM input by filtering the Camshaft Position
(CMP) sensor pulses when the engine is running and CKP sync pulses are also
being received. The PCM uses the camshaft position PCM input pulses to initiate
sequential fuel injection and to determine crankshaft position for the misfire
diagnostic. The PCM constantly monitors the number of pulses on the camshaft
position PCM input circuit and compares the number of camshaft position PCM
input pulses to the number of 1 8X reference pulses and the number of 3X reference
pulses being received. If the PCM receives an incorrect number of pulses on the
camshaft position PCM input circuit, DTC P0341 will set and the PCM will initiate
injector sequence without the camshaft position PCM input with a one in six chance
that injector sequence is correct. The engine will continue to start and run normally,
although the misfire diagnostic will be disabled.

Conditions for Running the DTC
The engine is running (3X reference pulses are being received).

Conditions for Setting the DTC
• The ratio of 3X reference pulses to Cam pulses received by the PCM does not
equal 6.

• The ratio of 3X reference pulses to 18X reference pulses received by the PCM
equals 6.

Above conditions for 80 occurrences.

Action Taken When the DTC Sets
• The PCM will illuminate the MIL during the second consecutive trip cycle in
which the diagnostic test has been run and failed.

• The PCM will initiate injector sequence without the camshaft position
signal with a one in six chance that injector sequence is correct.

• If equipped with traction control, the PCM will command the EBTCM via Class
2 serial data to set an ABS/TCS DTC, the EBTCM will turn OFF traction control,
and the EBTCM will illuminate the TRACTION OFF lamp.

• The PCM will store conditions which were present when the DTC set as Freeze
Frame and Fail Records data.

Conditions for Clearing the MIL/DTC
• The PCM will turn the MIL OFF during the third consecutive trip in which the
diagnostic has been run and passed.

• The history DTC will clear after 40 consecutive warm-up cycles have occurred
without a malfunction.

• The DTC can be cleared by using the scan tool Clear Info function or by
disconnecting the PCM battery feed.

Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through wire
insulation or a wire broken inside the insulation. Check for the following
conditions:

• Malfunctioning Ignition Coil. Remove the ignition coils and inspect the ignition
control module and coils for cracks, carbon tracking, or other signs that indicate
that the coil secondary circuit is arcing to the 1CM or 1CM wiring harness.
Refer to Ignition Control Module Replacement.

• Secondary ignition wire(s) arcing to wiring harness. Check secondary ignition
wires for carbon tracking or other signs of damage.

• Damaged harness. Inspect the wiring harness for damage.

• If the harness appears to be OK, disconnect the PCM, turn the ignition on and
observe a voltmeter connected to the CAM signal circuit at the PCM harness
connector while moving connectors and wiring harnesses related to the ICM and
the CMP sensor. A change in voltage will indicate the location of the malfunction.

Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may
help determine how often the condition that caused the DTC to be set occurs. This
may assist in diagnosing the condition.

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.

2. Ensures that the malfunction is present.

21. Determines whether the malfunction is being caused by a missing camshaft
magnet or a malfunctioning PCM. The voltage measured in this step should read
around 4 volts, toggling to near 0 volts when the CMP sensor interfaces with the
camshaft magnet.

22. This vehicle is equipped with a PCM which utilizes an Electrically Erasable
Programmable Read Only Memory (EEPROM). When the PCM is being
replaced, the new PCM must be programmed.

HTH. If you need more, just ask.

[1998RIVMAN]

Thanks!! I'll follow that through and see what shakes out.

Mike

[1998RIVMAN]

Well, I've visually inspected the area around the ICM and saw no visible carbon tracks or arc spots. Of course the voltmeter checks were good. ICM connectors checked out clean. The wire from the sensor to the ICM ohmed out good. Ground is good. I haven't pulled coils yet. Since that day, incidents have dropped off. Not completely but way down. I think that I will install new plug wires since I moved them slightly to get at the connector on the ICM. If that doesn't do it, then coils and ICM.
TBC.

[1998RIVMAN]

Ok, after having pulled most of my hair out, this is where I stand. Replaced coils and ICM (Thanks Ed), checked wiring and for arcing, NPF. Pulled scan of recent MIL using Snap ON MT2500. Freeze frame results are as follows:

P0341 CMP Sensor circuit out of range
Engine load 9%
coolant 198 f
ST Trim-1% -0.8
ST Trim-1 127
LT Trim-1% 2.3
LT Trim-1 131
MAP (kPa) 88
Engine RPM 1274
Veh Speed 43mph
MAF(gm/sec) 24.8
TPS % 13

Every time the code has set, the parameters are almost exactly the same.
No failures at idle, no failures at WOT. Can't get it to fail sitting still at all.

What am I missing? (Beside my sanity)

[1998RIVMAN]

Ok, I've ruled out all electrical problems except the +V supply to the crank and cam sensors. Since the crank sensor is OK, I am not holding much hope for that fault branch. I was talking about the problem with one of our master techs and he suggested that it might be a slack timing chain or walking camshaft. How prevalent are timing chain tensioner failures in the 3800 motor? I have only 44k on the engine and it was babied before I bought it.
The failure would seem to fit the slack chain scenario.

TIA

Mike

[1Hot97]

I wouldn't think a loose timing chain would cause this. Besides, a loose chain is more prevelant at idle, when the engine is under load, the chain doesn't have the same ability to flop around, IMO. It sounds like a possibly loose wire? Have you tried wiggling the wire bundles and connectors while the car is running?

[1998RIVMAN]

I'm going to get back into the harness this weekend. All ohmmeter tests so far have indicated no fault. The darn thing won't fail at idle or WOT, only light load such as maintaining speed and occasionally coasting. I need to get hold of a scanner that will capture a good amount of data so I can see what goes on when the engine starts coughing during that time. I'm beginning to wonder if I have multiple problems although the only code is the 341.
Thanks for the input.

[1998RIVMAN]

OK. I've been through every connector I can find and all the wires check out ok with ohm meter. My next step might be to replace the PCM.
One question that is nagging at me,.. can a failing crank sensor throw a p0431 code as well? The wording in the manual seems to imply that. ie. the cam sensor and the 18x reference don't match up. I recall seeing this somewhere on the web but can't remember where. I've had it stall lately pulling into my carport, no codes, starts right up. Sometimes it will miss at light load (1-4% TPS) and not set a code, other times it will set 341 pending ant not trigger the SES. I'm about ready to put a bullet in it.