Pcm testing

Tiny
ZEMORZEMOR
  • MEMBER
  • 2006 CHRYSLER PT CRUISER
  • 2.4L
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 95,000 MILES
What I should use to back probe the pt cruiser Pcm without damaging or spreading the connectors
Do you
have the same problem?
Yes
No
Wednesday, August 5th, 2015 AT 8:59 AM

22 Replies

Tiny
CARADIODOC
  • EXPERT
What are you trying to test? What symptom are you after?

The easiest way to back-probe a connector is to use a stick pin and go in through the rubber weather seal right next to the wire. I never approve of slicing off insulation from a wire because that will lead to corrosion and an broken wire.
Was this
answer
helpful?
Yes
No
+1
Wednesday, August 5th, 2015 AT 9:02 PM
Tiny
ZEMORZEMOR
  • MEMBER
I have a code p0882
The transmission control relay is used to supply power to the solenoid pack when the transmission is in normal operating mode. When the relay is off, no power is supplied to the solenoid pack and the transmission is in Limp-in mode. The relay output is fed back to the Powertrain Control Module PCM. It is referred to as the Transmission Control Relay Output circuit or switched battery.

After a controller reset (ignition key turned to the run position or after cranking engine), the controller energizes the relay. Prior to this the PCM verifies that the contacts are open by checking for no voltage at the switched battery terminals. After the relay is energized, the PCM monitors the terminals to verify that the voltage is greater than 3 volts.

The car goes to limp mode interminatley it wont shift to 2, 3, 4th gear it stays at 1st gear
so I want to check voltages at the pcm and at the connector of the solenoid pack
Was this
answer
helpful?
Yes
No
Wednesday, August 5th, 2015 AT 10:58 PM
Tiny
CARADIODOC
  • EXPERT
I see. You should also be able to monitor the voltage with a scanner. The problem is watching it for intermittent changes while you're driving.
Was this
answer
helpful?
Yes
No
Wednesday, August 5th, 2015 AT 11:08 PM
Tiny
ZEMORZEMOR
  • MEMBER
Ok like today I got off from work I start up the car and drove it to walmart about 10 miles the car was fine and it was no check engine light. When I got off from walmart I started the car I put it in drive the car shifted to first gear hard and the check engine light came on and it was not shifting to the other gears.
Was this
answer
helpful?
Yes
No
Thursday, August 6th, 2015 AT 11:22 PM
Tiny
CARADIODOC
  • EXPERT
That might be a good thing. This is a generalization, but worth considering. When the transmission starts out in first gear, up-shifts normally, then during or right after another up-shift it goes into limp mode, that is most often due to a slipping clutch pack. That means it's time to have the transmission rebuilt. You can verify that with Chrysler's scanner. It will show the "clutch volume index", (CVI). That's a set of four numbers corresponding to the volume in CCs that it takes to apply each clutch pack. An experienced transmission mechanic can tell how much life is left in each one based on those numbers.

When the transmission goes right to second gear before you're driving fast enough to warrant that up-shift, it is almost always due to an electrical problem. Most commonly that means a sensor or its wiring and connector terminals are suspect. That applies to code 882, but I don't have access to anything that gives the troubleshooting steps. You already have a better description for that code than I do.
Was this
answer
helpful?
Yes
No
Saturday, August 8th, 2015 AT 9:15 PM
Tiny
ZEMORZEMOR
  • MEMBER
Sometimes others codes show up.U0101 and p1603
Was this
answer
helpful?
Yes
No
+1
Sunday, August 9th, 2015 AT 7:57 AM
Tiny
ZEMORZEMOR
  • MEMBER
I went to oreilly auto parts and the guy scanned the car it was u1414 u 1415 p0218 p0882 but he scanned the computer as 2004 pt cruiser are those codes significant or does the car needs to be scanned as 2006
Was this
answer
helpful?
Yes
No
-1
Wednesday, August 12th, 2015 AT 8:21 AM
Tiny
CARADIODOC
  • EXPERT
I'm not familiar with "U" codes, but I do know that 2004 was the first year that a few models started changing over from the OBD2 to the new "CAN BUSS" emissions system. I don't know if they kept the same code numbers. Regardless, I don't think their code reader would have connected and communicated with the wrong system.
Was this
answer
helpful?
Yes
No
Wednesday, August 12th, 2015 AT 11:41 PM
Tiny
ZEMORZEMOR
  • MEMBER
For the code p1603 I mitchell1 says I need to check fused ignition switch circuits F202 and circuit F924 I looked at the computer diagram I did not see those circuits
how can I find them in Diy?
Was this
answer
helpful?
Yes
No
Friday, August 14th, 2015 AT 7:58 AM
Tiny
CARADIODOC
  • EXPERT
The problem is in some places, Mitchell just uses color designations, and in other places they use Chrysler's designation system. When they just give wire colors on their diagrams, you have to also use a Chrysler service manual unless you can look at the ignition switch and figure out which wire color you're after.
Was this
answer
helpful?
Yes
No
-1
Friday, August 14th, 2015 AT 2:03 PM
Tiny
ZEMORZEMOR
  • MEMBER
Can you please tell me how to check power and ground of the pcm?
Was this
answer
helpful?
Yes
No
Tuesday, September 1st, 2015 AT 8:06 PM
Tiny
CARADIODOC
  • EXPERT
I remove the connector's cover, then stick a pin through the rubber seal next to the wire. That pin provides a solid test point that I can connect a small clip to that can be connected to the meter's probe.

Be aware that when no current is trying to flow in a circuit, there can be high resistance in it, as in corrosion between two mating connector terminals, or all but one strand of wire broken in a wire. That high resistance is similar to standing on a garden hose. You'll still have full pressure at the nozzle as long as it's closed, but if you open it and try to get water to flow, your foot adds resistance, and the pressure at the nozzle will drop.

Voltage is electrical pressure. If there is high resistance in a 12 volt feed wire, you'll still measure 12 volts at the computer as long as the computer is turned off and no current is trying to flow. For your voltage readings to have the most validity, they should be taken when the computer is operating.

If you find 0 volts where there should be 12 volts, that obviously is a problem, but when you find 12 volts where you expect it to be, THAT'S where you want to be sure. One way to do that is to add a 12 volt light bulb to the circuit while you're taking that voltage reading. The bulb will insure there is current flowing in the circuit, and that will make any high resistance show up as the voltage goes lower.

There typically are up to four 12 volt supplies to the Engine Computer. One will be there all the time to keep the fuel trim, minimum throttle, and diagnostic fault codes in memory. One comes right from the ignition switch to tell the computer to wake up and do its thing when the ignition switch is turned on. When the automatic shutdown, (ASD) relay is turned on by the computer, it sends 12 volts to the ignition coil(s), injectors, alternator field, oxygen sensor heaters, fuel pump or pump relay, AND back to another terminal for the Engine Computer so the computer can verify that relay turned on. That 12 volts is the power supply for some circuits run by the computer. There is usually another 12 volt wire coming from a part of the system that needs a constant, steady charging voltage. That 12 volt terminal is the reference voltage for the charging system's voltage regulator. GM taps off the instrument cluster when they have a digital dash. That is to reduce flickering due to unstable charging voltage. If there's a problem with that circuit, charging voltage will usually be too high. It should be between 13.75 and 14.75 volts. By the way, all those places where I said you should find 12 volts, "12" is the generic value in a 12 volt system. In reality, with the engine running, the battery voltage should be between 13.75 and 14.75 volts, and that voltage is also what you should find at all four terminals at the Engine Computer.

Ground wires pose an additional problem because they end at a terminal bolted to the body where rust can develop on the body sheet metal and the wires can corrode where they're crimped in the metal terminal. All of that is exposed to the elements. If you try to measure them for continuity with an ohm meter, the meter's leads can have a few ohms of resistance, and that can mask one or two ohms of resistance in the ground wire. Where the voltage would drop in a 12 volt feed wire due to resistance, the voltage will rise in a ground wire due to resistance. If all but one strand of wire are broken in a ground wire, it will still read okay with an ohm meter, but the high resistance will cause a voltage drop when current is trying to flow through it. Therefore, a voltage reading on a ground wire is much more accurate than a resistance reading.

There is another potential problem the engineers foresaw and addressed. Ignition coils and injectors draw very high current for very brief periods of time when those items fire. Those pulses of high current will cause pulses of high voltage drops if there's excessive resistance in the circuit. Suppose that resulted in a pulse of 0.4 volts on a ground wire. If that is the same ground wire used by sensors, all of their readings will be high too. For example, at exactly half throttle, the throttle position sensor will read 2.5 volts. If there's 0.4 volts on its ground terminal, the signal voltage will go up to 2.7 volts. That is significant to the Engine Computer, but it is much more important to the MAP sensor's readings. 0.2 volts equates to a huge difference in fuel metering calculations.

To avoid this possibility, the engineers use four separate ground wires. Two are called "power" grounds, meaning they are for circuits that use a lot of power. That's the injectors, ignition coils, alternator field, etc. The other two ground wires are "signal" grounds, meaning ground circuits for sensors and anything else that would be adversely affected by slight changes in voltage. There's two of each wire in case one develops high resistance. If a pulse of voltage appears on a power ground wire, it will not have any affect on the signal ground wires. You can't measure those voltage pulses with a voltmeter. You'd need an oscilloscope to see them, but all that's good for is to see visually what you've already found with some other test.

To test the signal ground wires, the engine should be running, then measure the voltages on them. Ideally you should find 0.00 volts, but in reality, you might find a few hundredths of a volt. You can also measure on the ground wires for the throttle position sensor or MAP sensor, but due to the monitoring circuitry inside the computer, you can expect to find 0.2 volts on them.
Was this
answer
helpful?
Yes
No
Thursday, September 3rd, 2015 AT 11:38 AM
Tiny
ZEMORZEMOR
  • MEMBER
I did voltage drop ( engine running )for computer power and ground.
The computer has two power supply one off them is all the time hot the voltage drop was 0.05 v. The second power supply power up when the ignition is on or engine is running. When the engine is running the voltage drop is about 220mv. The voltage drop varies each time I start the engine sometimes it s 165mv sometime is 195 mv sometimes is 250mv. Between the positive battery and the computer pin there are a fuse 10 amp a connector and the ignition switch. I think there is an excessive voltage drop. How can I pint point the problem is it the ignition switch that is faulty or something else?
Was this
answer
helpful?
Yes
No
Monday, September 7th, 2015 AT 8:15 PM
Tiny
CARADIODOC
  • EXPERT
If you're measuring where I think you're measuring, 220 mv is not excessive. That is due to the normal resistance in the wiring.
Was this
answer
helpful?
Yes
No
Tuesday, September 8th, 2015 AT 7:54 PM
Tiny
ZEMORZEMOR
  • MEMBER
I did a voltage drop test between battery positive and pcm power pin the voltage drop was around 165 mv to 250 mv. The voltage drop for the other pcm power was 0.05v. For the ground side it was between 0.01 to 0.02 volt.
So you think is good?
Was this
answer
helpful?
Yes
No
Tuesday, September 8th, 2015 AT 9:38 PM
Tiny
CARADIODOC
  • EXPERT
Yup. No problem there.
Was this
answer
helpful?
Yes
No
Tuesday, September 8th, 2015 AT 9:57 PM
Tiny
ZEMORZEMOR
  • MEMBER
Yesterday I had another code p0562 low system voltage. How to troubleshoot?
Was this
answer
helpful?
Yes
No
Friday, September 11th, 2015 AT 6:36 AM
Tiny
CARADIODOC
  • EXPERT
First measure the voltage between the alternator's output terminal and the battery's positive post with the engine running. That voltage must not exceed 0.4 volts. If it does, there's excessive resistance in that circuit or there's some aftermarket item on the car that's drawing more current than the alternator is designed to deliver.

Next, measure the voltage between the alternator's housing and the battery's negative post, again, with the engine running. That voltage should not exceed 0.1 volt.
Was this
answer
helpful?
Yes
No
Friday, September 11th, 2015 AT 7:43 PM
Tiny
ZEMORZEMOR
  • MEMBER
I measured the voltage between the alternator's output terminal and the battery's positive post with the engine running and loaded ( headlight on, ac on ect). The voltage was 0.22 volt
I measured the voltage between the alternator's housing and the battery's negative post with the engine running and loaded ( headlight on, ac on ect). The voltage was 0.06v.

Also I measured the voltage between the positive terminal of the starter and the positive post of the battery when cranking the engine ( I push all the way down the gas pedal to prevent the engine from starting) the voltage was 0.1 vot

i measured the voltage between the negative terminal of the starter(case) and the negative post of the battery when cranking the engine ( I push all the way down the gas pedal to prevent the engine from starting) the voltage was 0.26v
are the numbers in spec if yes what the next step please?
Was this
answer
helpful?
Yes
No
Sunday, September 13th, 2015 AT 12:34 PM
Tiny
CARADIODOC
  • EXPERT
Sorry that I didn't see this a long time ago. Have you solved the problem?

The voltages you listed look okay. For the starter circuit, you're allowed up to 0.2 volts per mechanical connection, (such as where a cable is bolted to a stud or battery post), and no more than 0.4 total in the entire positive side of the circuit, and no more than 0.4 volts total in the entire negative half of the circuit. Those voltages have to be measured during engine cranking.

For the charging system, the same 0.2 volts applies but those voltages are only valid when maximum current is flowing. You need a professional load tester for that.
Was this
answer
helpful?
Yes
No
Monday, November 9th, 2015 AT 10:05 PM

Please login or register to post a reply.

Recommended Guides