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Way to test ECM?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Johnny KIlo, Oct 12, 2015.

  1. Johnny KIlo

    Johnny KIlo Junior Member

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    I am getting P0010 and I have replaced the connector and tested the wiring to the ECM harness. When the car is in ready mode I am getting really low voltage, like .02. Per the TIS documentation of P0010 I should be getting be getting 5V or more. Based on physical inspection the connector was cracked and appeared to be bad but I removed the harness connector and I was getting low voltage directly on the wire. All of the fuses looked good at visual inspection.

    Im a bit stumped. I guess I shouldnt rule out 2 separate issues. I know which pins on the ECM correlate to the oil control valve. Is there a way to test the ECM? I have TechStream and VCI.

    Thanks.
     
    #1 Johnny KIlo, Oct 12, 2015
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Since you have the service manual documentation, there are several things you can do:

    1. Find the ECU wiring harness connector pins which drive the camshaft timing oil control valve and back probe while the connector is installed, to see what the voltage is there. That will help you to decide whether the problem is with the ECU or the wiring harness.
    2. You can use an oscilloscope to monitor the pulse waveform produced by the ECU to drive the oil control valve. That would provide further evidence which is better than #1 above.
    3. Apply 12V directly to the oil control valve terminals (see the repair manual for the correct polarity applied to the terminals) to see if the engine idle becomes rough or the engine stalls, which would demonstrate the valve is working.
    4. You can also do the resistance checks of the valve and wiring harness connectors.

    It would be very unusual for the engine ECU to fail so you need to thoroughly check the valve and the wiring harness first.
     
    #2 Patrick Wong, Oct 12, 2015
  3. epoch_time

    epoch_time Active Member

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    Hi Johnny.
    The cracked connector.. Is it at the oil control valve or the ecu ?

    If the bad/cracked connector is at the ocv. Do you think the 5volt side could have shorted to ground momentarily or longer and blown the 5 volt source within the ecu? Is 5 volt line switched or continous source of 5 volts? Better check the continuity of the oil control valve (provided its a two wire device)... it should be an easy check. it should show I'm guessing probably 100 to 500 ohms? If not the coil is probably open...
    If coil (ocv) is good. and you know for sure there is no 5 volt source. Then the problem is inside the ecu.. could be a soldered in fuse, voltage regulator (7805 3 pin regulator), or transistor blown.. All are three dollar items. Finding a qualified bench technician to open ecu and find the blown item could be difficult... I'de bet a seasoned tv repair person could do it. Other wise recking yard. or other used source...
    I know the techstream will read vvt angle.. and most likely will allow activation of ocv..

    ----------------------------------------Apparently all the below will also cause p0010 code..
    But I think you are passed all of these looking for 5 volt source...


    - Dirty Oil
    - Variable Valve Timing (VVT) circuit is open or shorted
    - Oil Control Valve (OCV) circuit is open or shorted
    - Faulty variable valve timing (VVT)
    - Faulty oil control valve (OCV)
    - Damaged ECM

    Read more: P0010 2005 Toyota Prius Camshaft Position 'A' Actuator Circuit Bank 1 OBDII Engine Light Trouble Code | Engine-Codes.com

    hope this helps and good luck
     
    #3 epoch_time, Oct 12, 2015
  4. Johnny KIlo

    Johnny KIlo Junior Member

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    As always thanks Patrick. II took similar but not quite exact measures to what you described. With the engine I remove the E4 plug from the ECM and connected a AAA battery, it carried ~.5 vokts all the way to the connector so I am confident in my wiring and connector. I did not try with E4 ECM harness connected and the car on, I didn't think my leads would connect then I realized there were removable plastic pieces on them. I'll try this tomorrow.

    This issue is 2nd on my list now. I was troubleshooting a coolant near my water pump and broke off 2 bolts trying to make sure they were tight. I'm talking like a half a turn and it snapped clean off, on 2 different bolts. They appeared to be rusted. But I digress, I'll will test at the harness while connected tomorrow. Looking online ECMs appear to be rreallyt cheap, around $25 so I'm jus going to order one.
     
    #4 Johnny KIlo, Oct 12, 2015
  5. Patrick Wong

    Patrick Wong DIY Enthusiast

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    A good idea to use a battery. A new AAA battery produces ~1.6V open-circuit. When using your multimeter to measure voltage across the battery, what is the reading?

    If there is a big difference between the reading across the battery and the reading at the other end of the wiring harness, then the wiring harness has a problem.
     
    #5 Patrick Wong, Oct 12, 2015
  6. Johnny KIlo

    Johnny KIlo Junior Member

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    Thanks epoch. The cracked connector was at the OCV side. In fact it was so damaged there was no clip (it is the same connector at the S20, T2 and W3 connectors according to the TIS wiring diagram based on part number), so there is a good chance I inadvertantly plugged it in backwards shorting something out.

    I was getting continuity on the OCV sensor itself. I dont recall the resistance but I believe it was low, like 5 to 7 ohms. I'll check again tomorrow.

    I tried to determine the power path from wiring diagram but couldn't decode it. I believe the fuse sits between the battery and the ECM on the positive and the ECM connects directly to the harnesses. I could be wrong but based on the fuse block location (driver side) and the wire harness to ECM location (passenger side) it seems at least plausible. I did check every single fuse and relay and they all looked good physically. I also closed the circuit by looping the + and - connectors on the ECM harness side with a piece of wire and measuring continuity on the sensor side while removing each fuse, I never lost continuity, although it fluctuated, so the circuit stayed closed further supporting my statement above.

    Based on the wiring diagram I believe I should have ~5 v constant to the OCV while in IG ON. This was not the case and I know my wiring and connectors are good as I described in my response to Patrick. My understanding is that the OCV operates at 4.5 v or 5.5 v indicating it would open or closed.

    I strongly believe it's the ECM and I likely shorted it myself accidentally. Seems as if there may be other issues given that however.

    Are there typically any additional measure required when replacing an ECM beside phyisvcal replacement and coinnection? I have a smart key but I believe the smart key ECU and immobiliser take care of that programming.
     
    #6 Johnny KIlo, Oct 12, 2015
  7. Johnny KIlo

    Johnny KIlo Junior Member

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    Yeah I was expecting 1.5 v as well but the battery is used and its from Harbor Freight and likely cheap. I tested the voltage before connecting to the harness and received about the same voltage, a little less in fact if I recall.
     
    #7 Johnny KIlo, Oct 12, 2015
  8. Johnny KIlo

    Johnny KIlo Junior Member

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    well my issue is gone, cant definitively say what fixed it. I did replace the harness and ran new wire. I close the circuit at the ECM harness end with some loose cooper and got continuity on the sensor harness so my wiring and harness were good. I was still getting the same code so I ordered a replacement ECM. Got a coolant leak, ended up replacing the bolts and gasket on my water pump and when I got it running the code never came back, I even passed emissions. I disconnected 12v and HV (by removing the orange plug) when doing the water pump work and it was disconnected for about 3 weeks so maybe something reset?

    Either way thought Id close the loop, thanks for the help
     
    #8 Johnny KIlo, Nov 5, 2015
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