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cadillac Srx 3.6 (po203 injector circuit fault )


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tech72
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May 27, 2013, 11:20 AM

Post #1 of 30 (10976 views)
  post locked   cadillac Srx 3.6 (po203 injector circuit fault )  

I am working on 2005 srx Cadillac with a 3.6 . has a service code po203 Injector circuit fault . I have swapped injectors from cylinder to cylinder prob stayed a cylinder #3. Traced wiring from ECM to injector, checked for shorts. Not real familiar with the traction control system, but I know it will cut injector out at times. Can any one help.


Discretesignals
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May 27, 2013, 2:15 PM

Post #2 of 30 (10952 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

Does the engine have a misfire along with the injector circuit code?





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tech72
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May 27, 2013, 2:46 PM

Post #3 of 30 (10943 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

Yes , all miss fires are # 3 .I have also checked wave form with a scope , all but #3 show a signal.


Hammer Time
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May 27, 2013, 3:05 PM

Post #4 of 30 (10940 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

What's missing, the power feed or the ground pulse to that injector?



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tech72
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May 27, 2013, 3:14 PM

Post #5 of 30 (10935 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

control from ecm ( ground )


Hammer Time
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May 27, 2013, 3:15 PM

Post #6 of 30 (10932 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

Have you tried for a signal coming right out of the PCM?



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tech72
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May 27, 2013, 3:19 PM

Post #7 of 30 (10927 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

yes I have back probed that wire right at the ecm , also checked for a pulse ,that i for got to mention.


Hammer Time
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May 27, 2013, 3:20 PM

Post #8 of 30 (10922 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

And the result of the test was?



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tech72
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May 27, 2013, 3:24 PM

Post #9 of 30 (10915 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

no signal . with car running that wire has 12 volts .


Hammer Time
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May 27, 2013, 3:28 PM

Post #10 of 30 (10909 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

That pretty much means you have a bad PCM. I doubt it's the driver itself since it's capable of recognizing that the signal is missing but is probably a bad solder joint to that pin internally. Could be the driver though. Either way, it's a new PCM.

Just make sure that injector wasn't shorted to cause the failure in the first place.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on May 27, 2013, 3:28 PM)


tech72
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May 27, 2013, 3:30 PM

Post #11 of 30 (10904 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

with key on engine off wire or circuit has o volts show no short to ground or power .with key on engine off other injector circuits show between 2.6 and 3 volts.


tech72
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May 27, 2013, 3:43 PM

Post #12 of 30 (10899 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

I was leaning toward a ECM , but was not sure if was missing something thanks for the helpWink


tech72
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May 27, 2013, 3:45 PM

Post #13 of 30 (10894 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

do you think a used ecm could be reprogrammed or flashed .


Hammer Time
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May 27, 2013, 3:45 PM

Post #14 of 30 (10894 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

That makes no sense. With the key on you should be reading 12v through any of them because you are reading the power supply through the injector until it is grounded.



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Discretesignals
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May 27, 2013, 3:51 PM

Post #15 of 30 (10888 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

Also the PCM will disable that injector's driver if it detects a short in that circuit.


Quote
I doubt it's the driver itself since it's capable of recognizing that the signal is missing but is probably a bad solder joint to that pin internally


If the driver (transistor) is bad, the PCM will assume the circuit is either shorted or open. It doesn't monitor the transistor directly, but the circuit itself using a voltage feedback circuit. The PCM checks the voltage drop, just as you would with a volt meter. If the transistor doesn't, ground the circuit, the PCM will see 12 volts sitting at the feedback point and assume the circuit is shorted to power.

If the transistor is commanded off and the PCM sees 0 volts, it assumes the circuit is open or shorted to ground. The PCM doesn't know if the driver is the problem, it just knows if there is a problem in the circuit itself that the driver controls.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on May 27, 2013, 3:59 PM)


Hammer Time
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May 27, 2013, 3:55 PM

Post #16 of 30 (10883 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

That would have to be a short to power, not a short to ground and he has already tried swapping the injector.

He could always try cutting the wire and testing the signal out again.



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tech72
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May 27, 2013, 3:56 PM

Post #17 of 30 (10879 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

I am using a flow chart from mitchels , and one of the steps says to check for between 2.6 and 4 volts with key on engine off, that circuit is the only one that shows 0.


tech72
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May 27, 2013, 3:59 PM

Post #18 of 30 (10873 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

That is also with the ecm plugs removed , checking that pin .


Hammer Time
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May 27, 2013, 4:04 PM

Post #19 of 30 (10868 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

That test is with the harness connector to the injectors unplugged and if you read the response to that test for that result, the next step is replace the ECM. (step 17)



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Discretesignals
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May 27, 2013, 4:09 PM

Post #20 of 30 (10862 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

If you have 12 volts at the PCM connector for #3 injector circuit with the key on, unplug the injector and make sure it goes to 0 volts, so you know the circuit isn't shorted to power.

If you have 12 volts sitting at the PCM, clear the code and crank the engine while using your scope to see if the PCM commands the injector circuit. If you don't see an injector ramp and your voltage remains at 12 volts the entire time, PCM is the culprit.

Like HT stated, since you swapped the injectors already, current ramp them and make sure your injector winding isn't shorted and using too much current and toasting the transistor in the PCM.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on May 27, 2013, 4:11 PM)


tech72
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May 27, 2013, 4:12 PM

Post #21 of 30 (10853 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

Again , I really thank you for your time and quick response. I am going to replace the ECM. I will let you know how it turns out. SmileSmile


Hammer Time
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May 27, 2013, 4:13 PM

Post #22 of 30 (10852 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

The flow chart he's using has already condemned the ECM.



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Discretesignals
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May 27, 2013, 4:18 PM

Post #23 of 30 (10845 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

Flow charts are useless most of the time....LOL

I haven't used a flow chart in years. Most of the time they either lead you into a loop or dead end or have you ripping the entire vehicle apart ohm checking wires. The engine controller doesn't ohm check wires, it makes its checks with the circuits loaded, so why would you want to ohm check wires using a flow chart or unload circuits and tests voltage at connections?

The only thing I use flow charts for is to get an idea what a particular circuit is doing. Other than that its understanding circuit design, doing voltage drop tests, and using the lab scope to see what is going on inside the circuit. There ain't no way a flow chart is going to help you find a glitch that may occur in a few milliseconds.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on May 27, 2013, 4:22 PM)


Hammer Time
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May 27, 2013, 4:21 PM

Post #24 of 30 (10836 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

This one was a pretty clear "go/no go" test.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Discretesignals
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May 27, 2013, 4:32 PM

Post #25 of 30 (10830 views)
  post locked   Re: cadillac Srx 3.6 (po203 injector circuit fault )  

No it wasn't. It never had you check for a shorted injector that could have took out the driver in the first place. The next poor idiot would have replaced the PCM and fried the driver in it because the injector was shorted.

Also what happens if the problem is intermittent, like a poor connection in a inline connector? Remember PCM sees an open for more than 4 seconds and it turns off the transistor. You go to check it and see that everything up to the PCM is fine and conclude the PCM is the culprit. Then you find out later that the PCM was doing what is was supposed to and it wasn't the problem after all. You have a pissed off customer and you wasted all the time misdiagnosing it.

You gotta think outside the box because most of the vehicles you run into, the flow chart is going to stick it in your butt. Like I said the flow chart is great for understanding circuit design, but as for the all great troubleshooting bible, it ain't going to happen.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.






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