RobZ

My brother bought a 98 z28 cheap,but has some problems.
We pulled the P0342 code Camshaft position sensor Circuit A - Bank 1 Circuit Low Input.Car starts but stumbles and kind of hard to start.So I went ahead and replaced the Camshaft Postion sensor only to run into the same problem.What can I do to further diagnose the problem?Any Ideas?

2fast97Z

iTrader: (20)

let me run that code on my Solus Pro in the Morning and i will pm you

v8

iTrader: (10)

cam shaft postion sensor A

Manic Mechanic

iTrader: (3)

Code P0342 in 98 5.7, other years similar. The PCM uses the cam sensor to determine firing order on start-up, without good signal the PCM reverts switching firing order back and forth between 180* out and right while watching the MAF sensor. When it sees the MAF signal pick up sharply it sees "engine started" and leaves the firing order there until the next shut down. For some reason the PCM is not processing a good camshaft position sensor (CMP) signal. This could be caused by serveral things.

Defective sensor (not likely now with new one but still possible)
sensor 3 wire circuit missing power or ground from PCM
wiring problems (open, shorts, poor connections)
defective PCM (circuit works computer doesn't)
engine mechanical problem (camshaft or engine wear, wrong cam like for a LS2 where the sensor is in front)

Before I spend a lot more time descibing the wiring and diagnostics do you have a DVOM and a basic knowledge on how to use one? Can you test for voltage, OHMS, continuity, duty cycle, etc? Well hopefully so because I ended up typing it out anyways. If not find someone who does or take it too a pro before you break something lol. Have fun, this is what I do for a living. Hopefully you can understand it and it helps you find the problem. Not responsible for damages. Always disconnect your battery before diconnecting PCM from harness.

First off was the bottom of the old sensor physically scraped, bent, or otherwise wacked on? If it was pull you new one and check to see if it's now busted up also. If so you have internal engine problems that are taking out the sensor by contact. If not you should pull the connector off the sensor and look at the terminals carefully. Look for a loose fitting, bent open, or missing terminal. There is a jumper or splice for this circuit on this car near the EGR valve, open it and check both sides of the splice connector just the same. If it's already unplugged there's the problem.

There are three wires in this circuit. Tests for voltage, grounds, and signal are all with the key on. Corrosion in any conector or along any wire is a give away as to a problem and should be corrected or repaired first.

RED is BATV+ from the PCM, with the jumper splice reconnected you should have BATV+ at the red wire terminal in the CMP connector when grounding the DVOM on the battery ground terminal.

PINK/BLACk is the ground for the sensor, it grounds in the PCM. You should be able to see the same voltage as testing above but using this terminal to ground your DVOM.
If either or both fail this test pull the PCM and disconnect the wire harness and check these circuits for continuity. Look at all the pins and make sure they are all there and straight. If the circuits are all sound from PCM to sensor connectors and you don't have one or both voltage and ground then it's a bad PCM.

If both are good you can tap into the circuits signal return wire BROWN/WHITE with your DVOM (anywhere along the circuit but near the PCM connector is best) with your DVOM grounded to BAT- check DC voltage duty cycle with all reconnected and the engine running at idle it should be 45% to 55%.
If no signal and power and ground are still good check for continuity from the CMP sensor connector back to your tap. If no continuity find and repair the open circut. If signal is good then check for continuity from the PCM connector pin to your tap. If no continuity find and repair the open circut.
If all is good in the circuit with a bad or missing signal you have a defective sensor or internal engine problems that prevent the sensor from generating a good signal, like wrong or bad cam, i/e missing reluctor (trigger) wheel, out of place (timing gear walked forward), or similar.
If you do have a proper 45-55% duty cycle on this circuit pull the PCM and check the signal return circuit BROWN/WHITE pin for damage or missing, then check for continuity from the PCM connector to the CMP sensor connector. If you had a good duty cycle signal and the wiring is all good from connector to connector you have a defective PCM.

Internal engine mechanical problems can be verified by removing the CMP sensor and looking down the hole, perferably with a boreascope but possible with a mirror and light. Crank the engine while looking, you should see undamaged metal passing the hole 50% of the time. If more or less it's mechanical.


Vernon

RobZ

Manic Mechanic,Wow are you a Master Tech?Thanks to you and everybody else for the responses.I must also confess some left over things I did not describe.

The engine also appears to have lifters issues,but I taught well if I can fix the P0342 code by replacing the Cmp sensor that might take care of the problem.Apparently it did not.Im not as knowledgeable as you Manic Mechanic,but I do understand checking for continuity and power b+.I didn't do all that diagnosing.I did check the bottom of the old CMP sensor it looked fine.So apparently the reluctor wheel on the cam might be bad or a short,open circuit,bad pcm.

Might be just a mechanical problem I do hear lifters that seem to be out.It could also be a bad cam.Thank you for the info man.Its most appreciated.

Fast98Z

iTrader: (1)

I am having the same issue with this. Did you ever figure out the issue?

FireHawk178

iTrader: (9)

'08 doesn't seem like it was 5 years ago.

mjcotroneo

iTrader: (12)

the ground and harness on the back are notorious for chaffing. pull back the wire loom and check for chaffing or open wire. if so get a pigtail and splice it in or fix the harness using weather proof connectors or heat shrink and solder.

Manic Mechanic

iTrader: (3)

Ha, I was wigging out. I thought, "Wow, somebody answers tech question posts just like I do." So I scroll back up and it was me. LOL. So then I'm like, holy crap I did that in DEC and don't even remember it, pretty good work if I was drinking. Then I read why it's back up this month and Firehawk178 points out it's 5 years old. LOL again. Yeah I'm a Master Tech, isn't this obvious now? Haha
.

Good advice from mjcotrneo. If you don't find any chaffed wiring have you done the power and ground checks?

Vernon

mjcotroneo

iTrader: (12)

im a gm cert tech lol before i opened my shop i worked for gm (a lot of dealers during the our generations depression haha) for a while so i saw a lot of the same problems. lol good to know someone else chimes in to help people out when they have questions.

larryrhr

I'm a engine builder but not a obd2 guy. Have a customers 01 silverado 4.8 with p0342 code that is set pending immediatly on startup and then on second start sets code and mil. tach works. replaced cmp pigtail and checked cont from pcm to sensor, 0 ohms. replaced cmp sensor, had not hit, but replaced it anyway. look at reluttor with #1 tdc in firing position and compared with old cam. same indexing and centered in cmp cavity. started checking live harness, have batt voltage at all pcm power supply wires but 1 volt less at red wire to cmp sensor. can this cause problem? dont have a duty cycle meter so I hooked up cmp to harness with key on and checked voltage on brown wire at pcm, .2 volts and then pass metallic object across sensor and switched to .7 volts. voltage will only change when passing the object the opposite way past the sensor mimicking the reluctor wheel. seems like everything is doing what it is supposed to do. only non stock internals are comp cam, 510 lift, 202-212 dur@50and 116 centers, nothing crazy. only symptoms are hard start cold occasionally and hard start warm occasionally. good power and drivability, very slight rough idle at times. going to put a tune on it but need to resolve this first. I am ready to condem the pcm but need some input first. hate replacing pcm and not cure problem. Batt only drops to 10.5 when cranking, appears good, charging system above 14.5.
,

Manic Mechanic

iTrader: (3)

This post will not die.

On the latest question for the 2001 truck, all of your voltage readings are fine. The one volt drop going through the PCM is totally acceptable and worries me none.

Many automotive DVOM's have duty cycle, ask a few buddies and you'll probably find one.

A few things other than PCM that I came up with.
1. The CMS isn't close enough to the cam reluctor and isn't reading consistent. The PCM likes 50% duty cycle. You have tach so there is some switching going on. Check to make sure the block doesn't have any grease or dirt on the mounting pad of the CMS that's keeping it from seating fully. Look for an old seal or foreign object in the bore. As close as you can get without ever hitting is best. Clean the block and sensor retainer. Peer down at the cam while turning the crank by hand to be sure the cam isn't damaged or manufactured incorrectly. Should be 50% metal and 50% blank with clean edges and surface.

2. Another tech reported finding the Brown/White signal circuit wiring rubbed in the left hand wheel well area beneath the fuse box. Follow the harness from sensor to PCM looking for any area of contact or extreme heat. I had one that was melting against a manifold where it was hard to see drive me nuts for most of a day.

3. EMI interference. While your looking along the harness note any aftermarket wiring that may be ran alongside or near the engine harness. The spark cables also will screw things up sometimes.

Vernon

cdk4219

Ok just went through this and thought I would reply what my fix was. I have a 98 ls1 that I had the p0342 code, sometimes it would start right up, sometimes crank forever. After doing all of the stuff, I found that the cmp jumper connector located by the egr was unplugged. I never knew what that 3 wire connector was for, but on the 98 it is a diagnostic jumper. It seems that the cmp sensors are pretty stout and don't fail that much, so usually this is a wiring issue. To add to the problem the jumper isn't in the wiring diagram. Make sure someone didn't accidentally unplug the jumper connector.

enigmah

iTrader: (1)

When I had this issue with my v6 FB swap I was running into that same issue - Found out my problem was simply not plugging in two connectors on the passenger side of the fuel rail that I thought were useless. I would double check for any shorts there

ramairws6

iTrader: (33)

Is this so called "jumper wire/connector" only on the 98 cars or is it on all the newer F Body's also?

cdk4219

Seems like a 98 only ls deal with f body harness, but as above I thought it was useless, little did I know it would consume 20 or more hrs of my time

UR50SLO

iTrader: (3)

We did a swap from a 99 WS6 T/A and 6spd into a 66 GTO Convertable. Had this exact same problem like cdk4219 had stated. Sometimes starts right up... other times would pop out exhaust with extended crank time. Could not figure it out... Did a pinout at ecm.. all good... 2 different sensors.. Nothing seemed to change it... stayed that way for the last 4yrs.
Just finished a 98 LS1 down into a 69 Camaro... Same issue!!!! GRRRRRRR...
Had the same guys weed the harness.
CDK4219's post here key'd me into that plug... It was nowhere to be found on the weeded harness. So I called the guy who did the harness and inside that blank plug it FLIPS the Cam signal. IF that plug is gone or the wires are weeded out you have to swap the A and C Pins.
With out doing that A-C pin swap it will not start correctly.
So We had the guy with the 66 GTO come over and swapped the pins while he waited and it fired up 10x's in a row.... So THANK YOU For this thread!
~Scott

Smile_E_Face

Had the same symptoms with my 98 LS1 Camaro with both P0341 and P0342 codes. Replaced the cam position sensor and the P0341 code went away but the P0342 code was still active. Found this thread and started looking for the 3-wire connecter then found the frayed Brown+white wire coming out of it. I solder/heat shrinked the wire and the P0342 code went away. Now my car drives like it should again

Thanks for the information on this thread guys

chvycmaroz28

iTrader: (1)

do u have a picture of this jumper ur talking about?

fst100

iTrader: (5)

Resurrecting this thread, Bump for pics too!