06 CTS, No Crank, No Communication with ECM, U1000
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So you have communication with other modules through CAN lines (but no with ECM) and the other modules are telling you they don´t have communication with ECM through class 2?
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what is resistance between can lines at ECM? I mean, CAN-H and CAN-L unplugged from the other modules? If you have 120 ohms, you need an additional 120 ohms resistor, so that you can simulate total 60 ohms in CAN network.
If you have no activity, i would replace ECM.
Is there any CAN expert with a second opinion?
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When I check pins 6 and 14 for ohms it is open.
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1. As Cheryl said, ECM is using two different protocols.
2. Class 2 (J1850 VPW). All modules (except TCM) are connected to ECM through this network). Class 2 is assigned to (pin 2 at DLC).
3. CAN (ISO XXXX). ECM & TCM are directly connected, sharing data each other (pins 23 & 55 in ECM and 32 & 33 in TCM). There is a second CAN network shared with DLC (pins 33 & 53 in ECM and 20 & 21 in TCM). CAN is assigned to (pin 6 & 14) at DLC
4. CAN network total resistance is 60 ohms (so resistance between pin 6 and 14, should be 60 ohms) with ECM & TCM plugged
5. If you unplug TCM, resistance between pin 6 and 14 at DLC should be 120 ohms (resistance inside ECM). if you can stablish com with scanner, TCM is likely the problem
6. If you unplug ECM, resistance between pin 6 and 14 at DLC should be 120 ohms (resistance inside TCM). if you can stablish com with scanner, ECM is likely the problem
7. As Cheryl said, scope is needed to check voltage and waveform (with multimeter you cannot verify lower and higher voltages, neither square signals)
Bearing in mind that class 2 network is also having issues and the fact TCM is not connected to class 2 network, I would say ECM is the problem.
BTW. Are you having communication with TCM?
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I did not realize when I checked the ohms on 6 & 14 yesterday that my dad had the TCM disconnected.
I have 7 mega ohms on 6 & 14 everything connected.
With the TCM disconnected I have infinite ohms.
With the ecm disconnected I have infinite ohms.
Yes, I can communicate with the TCM.
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- Hardtopdr2
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1. can key be turned to acc, off, run, and crank positions? Another wire to check would be (if it applies) module wake up signal wire to ECM so if key can't be turned it may be in power down mode. Though doubtful
2. Have you tried to run a separate pair of wires to dlc from ecm can high and low to eliminate a almost completely cut wire?
3. Using wiring diagrams look at the communication network diagrams and see where the wires from the ECM tie in for each module that can't communicate with ecm. Then load test those circuits with them unplugged from those modules to see if you get a dim light on one or more sections. Load test with a 4 amp bulb and a jumper wire to battery negative and the load test bulb to positive. Compare brightness to when it's hooked to the battery itself. Just remember continuity/ 0 ohms can happen with just one strand of wire intact.
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2. No I have not. I have a feeling I have a wire that has been chewed in two.
3. I'll do that next.
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- Hardtopdr2
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Will the headlight test work on the can bus? Is the can bus too low of voltage to illuminate a headlight?
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