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Dan, ASE Certified Technician
Category: Chevy
Satisfied Customers: 2270
Experience:  20 Year Factory Trained Current GM Technician
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2003 Malibu: V6..cranking but wont start at all..throttle body

Customer Question

2003 Malibu 3.1L V6 cranking but no start problem started on cold damp mornings turned into cranking but won't start at all. No start is spark related (fuel pump kicks in in "on" position and sprayed quick start in throttle body and still wouldn't start. New wires and good plugs. I have 12V at the ICM with the car in "on" I tested the crank sensor at the ICM it had proper resistance with increasing voltage while cranking (replaced the lower one anyway) I have correct ohms for wires as well as a secondary resistance of 5550 at all three coil packs. When I remove one of the coils and test the voltage there while cranking with a tester light there is no power there. I replaced the ICM and had identical results, returned the new ICM thinking it was a faulty part and the second new one was installed with the same results.

To the best of my knowledge this is not a Passlock problem, the car cranks, the theft light does not blink with a failed start. Even left the car in "on" for ten minutes and the light wouldn't turn off.

The car started giving me many problems Monday where it wouldn't start all day. I finally left the car in "on" for a minute or two and would start. This worked until Friday where the car would not start at all, when I finally got it started it ran fine until it stalled out twice on a busy street. Finally got it started up again, rushed home and it hasn't started since...

Submitted: 5 years ago.
Category: Chevy
Expert:  Dan replied 5 years ago.
My name is Dan

Turn the key on and see if the service engine soon light comes on and stays on before you try to start it.
Check this and let me know and we can go from there.
Customer: replied 5 years ago.
Turn the key to "on" without starting it turns on all lights and after the typical 3 chimes the only lights that remain on solid are Theft System, Oil Pressure, Battery, and the Engine light.

Service Engine turns off after the chimes and stays off.
Expert:  Dan replied 5 years ago.
Which crank sensor did you ohm? The one in the back or the one behind the crank pulley? this engine has 2 crank sensors
Check the wire that runs from the back crank sensor to the ignition module. Seen that wire not get attached right and gets too close to exhaust pipe and melt the wires. That can cause a start up at one time and a no start also.
Customer: replied 5 years ago.
I checked the crank sensor at the back (purple and yellow wires at ICM) that was the same sensor I had changed. I'll go out now and check continuity between the ICM connection and sensor if I can.

Is there anyway to rule out the second crank sensor or the cam sensor?
Expert:  Dan replied 5 years ago.
To check them, you would need a scan tool that can read data to see if they are reading rpm on the scan tool.

Check for resistance to ground on the purple wire or the yellow wire to the crank sensor.

check the ground doing to the ignition module on the black wire.
Customer: replied 5 years ago.
Ohm reading on new crank sensor (at back) is 952ohms (read from plug off ICM)
Purple wire to ground and yellow wire to ground were open.
Black wire on icm plug to ground is good.
Expert:  Dan replied 5 years ago.
How are you testing for spark?
Customer: replied 5 years ago.
Plug out of cylinder, in wire, pressed to intake.
Also tested with coil pack off, and tester light across both contacts on ICM while cranking. I'm on my way out now to get a spark tester.
Expert:  Dan replied 5 years ago.
Check it with a spark tester to make for sure.
We can check the other crank sensor but we may need a scan tool to watch data to see if the computer is getting a crank signal

check it with a spark tester and let me know.
Customer: replied 5 years ago.
Grabbed a tester (inline) tested front left plug and get a quick flash when first cranked and a quick flash during last rotation (after key is released). Nothing in between.
Expert:  Dan replied 5 years ago.
That normally means that one of the crank sensors are not reading right. You can check the power and ground to that sensor also. The connector is by the A/C compressor and the oil filter. Light green wire is the 12 volt wire and the yellow wire is the Low reference (Ground). The Light blue wire is the signal wire. There is not spec to ohm this sensor out. It is an Hall effect sensor.
then next step is to see if we are getting a crank signal on the data display of a scan tool.
Dan and 3 other Chevy Specialists are ready to help you
Customer: replied 5 years ago.
The light green wire is 10.8V (engine has been cranked a couple times today)and we have a good ground at the yellow wire. I'll have the scanner hooked up tonight or tomorrow and will let you know.
Expert:  Dan replied 5 years ago.
Ok with a scan tool, see if it indicates a 3X crank sensor signal during cranking.
Customer: replied 5 years ago.
Is that different than the 7x (purple/ Yellow)or the 24x (green/ blue/ yellow) crank sensor? Or does the scan tool lump all the signals in together under the same heading?
Expert:  Dan replied 5 years ago.
The rpm signal on the scan tool mainly uses the one behind the crank pulley,
There may be a line for the 7x or the 24x to display a yes or no you can watch while cranking. The data varied from year to year. But there should be a line for a 3x signal that the ignition module sends to the engine computer
I can send you the step by step diagnostic instructions for the ignition system if you want them.
Check the system for codes also.

Crankshaft position (CKP) sensors
The CKP sensor B is a variable reluctance sensor. The magnetic field of the sensor is altered by a crankshaft mounted reluctor wheel that has seven machined slots, six of which are equally spaced 60 degrees apart. The seventh slot is spaced 10 degrees after one of the 60 degree slots. This sensor provides the ignition control module (ICM) with 7X signals, or seven pulses for each revolution of the crankshaft. The pulse from the 10 degree slot is known as the sync pulse. Both of the sensor circuits are connected to the ignition control module (ICM). A signal converter within the ICM produces digital 3X output pulse to the powertrain control module (PCM), the 3X reference is known as the low resolution engine speed signal.
The CKP sensor A contains a hall-effect switch. A hall-effect switch is a solid state switching device that produces a digital ON/OFF pulse when a rotating element passes between the sensor tip and a magnet. This rotating element is called an interrupter ring or blade. In this case the interrupter ring has 24 evenly spaced blades and windows and is part of the crankshaft damper assembly. This sensor provides the PCM with 24X signals, or 24 identical pulses per crankshaft revolution. The 24X signal is used for enhanced smoothness and idle stability at a lower calibrated RPM. The PCM supplies the sensor with a 12-volt reference, low reference, and signal circuit.
Camshaft position (CMP) sensor
The CMP sensor signal is a digital ON/OFF pulse, output once per revolution of the camshaft. The CMP sensor does not directly affect the operation of the ignition system. The CMP sensor information is used by the PCM to determine the position of the valve train relative to the crankshaft position. By monitoring the CMP and CKP signals the PCM can accurately time the operation of the fuel injectors. The PCM supplies the sensor with a 12-volt reference, low reference, and signal circuit.
Ignition control module (ICM) and ignition coils
Three dual tower ignition coils are mounted to the ICM, and are serviced individually. The ICM performs the following functions:
- The ICM receives and processes the signals from the CKP sensor B.
- The ICM determines the correct direction of the crankshaft rotation, and cuts spark and fuel delivery to prevent damage from backfiring if reverse rotation is detected.
- The ICM determines the correct coil triggering sequence, based on the 7X CKP signal. This coil sequencing occurs at start-up, and is remembered by the ICM. After the engine is running, the ICM will continue to trigger the coils in the correct sequence.
- The ICM produces and inputs 3X reference signals to the PCM.
- The ICM contains the coil driver circuits that command the coils to operate.
Customer: replied 5 years ago.
A step by step would be excellent, if that is okay.
Expert:  Dan replied 5 years ago.
Click here for the file it should open up in a pdf file that you can print
Customer: replied 5 years ago.
Well we hit a snag... The car would crank but not start. I accidently left it in "on" went inside, came back out after 5 or so minutes and tried it for the heck of it and it started first try... (How it started all last week) I wasn't able to get any readings off the computer because it was running.

I turned off the car, reached down and unplugged the crank sensor behind the crank pulley and the car started after 1 try, I had no tach and it came up with the proper code P0336.

I drove it around the block twice, turned it off several times and it started first or second try.
Expert:  Dan replied 5 years ago.
Will it not start with the crank sensor plugged up?
Customer: replied 5 years ago.
With the crank sensor a (behind pulley) unplugged it started and gave me a P0366 code.
With crank sensor b (rear of engine) unplugged the car will not start.
Expert:  Dan replied 5 years ago.
The car must have the crank sensor B or it will not run

I you plugged up the front crank sensor, will it start?
Customer: replied 5 years ago.
I went back out, it started up first try.
I unplugged crank sensor "a" and than wouldn't start.

Plugged crank sensor "a" back in and it starts again.
Expert:  Dan replied 5 years ago.
You could have a wire shorting out somewhere or an intermittent crank sensor in the front or a cam sensor or the engine computer has an intermittent issue.
Make sure the cam sensor (under the power steering pump) wire is not rubbing on the pulley
Customer: replied 5 years ago.
Can a bad ignition switch cause this problem?
My friend came by again with his reader and it came up with a U1000 code. It started fine again this morning but died three times while idling in a parking lot and started no problem and drove home problem free.
Expert:  Dan replied 5 years ago.
I was asking about the service engine soon light at first because I was thinking ignition switch. A BCM can set a u1000 and cause this if it doesn't power up. Can your scan tool read bcm data?
does the power locks all work when it won't start?
Customer: replied 5 years ago.
The scan tool I have doesn't read BCM data. I would have to take it in to my mechanic. The power locks work when I have starting problems. Although if I crank too long the locks will click (probably voltage related)
Expert:  Dan replied 5 years ago.
The u1000 could be caused by another module not powering up or giving the right data or the battery going low.. Clear the code out and see if it sets when it wont start.
The ignition switch could be the cause but i normal find that the check engine light wont come on when you first turn the key on. You can pull the switch loose and check the wires at the connectors of the ignition switch to see if all keeps 12 volts on them. (Did the blower work when it wouldn't start) You can loosen up the switch and get to the connectors with the radio removed.
With you messing with the wires by that front crank sensor and then it starts, you could have a wire shorting out around there or the front crank sensor bad.
Customer: replied 5 years ago.
I'll check the switch tomorrow if I get a chance.
The blower (I'm assuming the heating/cooling fan inside the car) will turn on when switched on if the car won't start.

I'll clear the code and look for it after.
Expert:  Dan replied 5 years ago.
Ok let me know if you need further help
Customer: replied 5 years ago.
I pulled the ignition switch out tonight and some of the continuity points in my book (Haynes) don't match the switch.

As per my book there should be two points of continuity in the "acc" position and neither of them have continuity.

Two points in the "on" position don't have continuity when they should as per the book

And one point in the "run" position does not have continuity when it should as per the book.
Expert:  Dan replied 5 years ago.
I can tell you wire colors or pin # XXXXX the connectors that plug up to the switch to ohm out. Ohming out the switch is not a good test to tell if its good.
Customer: replied 5 years ago.
Sure I'll take those diagrams and check them tomorrow.
Expert:  Dan replied 5 years ago.
2 big connectors on switch
Red wire on each switch pin a should have power at all times This is the terminal you ohm them to on each connector.
On the natural color connector:
the orange wire pin c should have power in the run position ( or less than 2.0 ohms to pin a on the switch)
yellow wire pin B in the start position
dark green pin e In the acc- run and start position

on the black color connector:
pink wire pin B in the run and start position
brown wire pin pin c in the acc and run position

A voltage drop test is a good way to tell when its acting up. can check it when its not to make sure its not a problem with it. Place the volt meter to dc volts and hook one lead up to the battery positive post ( or back probe into the red wire at the switch) and the other lead back probe in the ignition switch connector of each of the wires listed above and turnt he switch to the correct position of the wire color and check the reading, You should have less than .5 volts. more than .5 volts is considered bad.
Customer: replied 5 years ago.
Removed fuel pump fuse for cranking.

Beige connector:
Orange wire pin C should have power in the "run" position. (12.09v)
Yellow wire in the "start" position (10.75v while cranking)
Dark Green in the "acc" (12.14v) "run" (12.09v) "start" (10.8v)

Black connector
Pink wire in the "run" (12.14v) "start" (10.8v)
Brown wire in the "acc" (12.15v) "run" (12.11v)

We metered the two red wires to ground and had normal battery voltage and dropped to 10.8v while cranking.
Expert:  Dan replied 5 years ago.
those are normal results but was the car acting up? Wait until it does not start and check it again.
Customer: replied 5 years ago.
Yes it's "working" currently. Stalling randomly (parked and while driving) but starts almost immediately afterwards. Will check next time it won't start.
Expert:  Dan replied 5 years ago.
Has it set any codes lately?
Customer: replied 5 years ago.
No P codes, haven't been able to check for that U code again (with my friends reader.
Expert:  Dan replied 5 years ago.
Check it when it acts up and let me know.
Customer: replied 5 years ago.
Drove the car to my mechanic Sunday night. Hasn't been able to start it since. He checked the switch and all the readings were fine. He pulled the switch apart and cleaned all the contacts.

Everything he checked was fine, except that today he hooked it up to his reader and while the car was in the "off position, the computer was telling the scanner that the fuel injectors were spraying.

The symptoms and odd happenings are.

No theft light
No spark at coils or plugs (other than initial and releasing of the key)
The car started once with the front crank sensor unplugged.
The u1000 code (that was cleared and came on again)
Crank sensors are sending signal to the computer.
and now the computer telling his scanning tool that the injectors were firing while the car was off.

He is convinced that the PCM needs to be done and suggested I get one from a scrap yard. My question is how close to my car does the pcm need to be? There is a Malibu at my scrap yard same generation, same engine/transmission but different interior package (leather with a different radio.) Will this swap or do I need to go new and get it programmed?

Expert:  Dan replied 5 years ago.
Some part stores can sell a new PCM that comes programed, You may have to perform a cranksensor variation learn on it with a scan tool.
A junk yard will have to be programed to your car by a shop that can do programing or a dealer.
Customer: replied 5 years ago.
Even if it's the same car at the junk yard it will need to be programmed? I figured it wouldn't know any difference.
Expert:  Dan replied 5 years ago.
The VIN # XXXXX XXXXX in the programing and it wont work unless the vin matches the other modules.

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