Hi all, a little background: Last week I started my truck (2005 SR5, AC, 4x2, Auto, 190k miles) and it instantly died. After 2 or 3 attempts it finally started but had a very bad misfire. I shut it off and when I hooked up my scan tool (to check the misfire) it started and ran fine. Ran good all that day, then did the misfire thing trying to start later again that night. After 2 or 3 attempts it quit cranking all together.
Here are the major troubleshooting steps I've taken:
Battery is a fairly new DieHard AGM and measures a little bit more than 12 volts. I'm using a Fluke 87, so i'm sure my readings are fairly accurate. I work as an industrial electrician in my day job.
If I pull the start relay and jump across it with a wire, the starter turns the engine fine. I think the starter is not the issue.
The start relay measured fine, but I swapped it with a spare just in case. No change, put original back.
If I pull that start relay and measure voltage across where the coil side would plug in I get about 8.5 volts in both run and start - very weird.
STA fuse is good and gets 12v to gnd when the key is turned to start.
I've checked all the fuses under the hood and under the dash.
I opened the fuse box under the hood to check for rodent damage (as in pulled from the inner fender, undid the clips and removed the bottom to look at the internal wiring). All looks good.
At this point I downloaded the FSM
I'm having trouble backprobing the ecu, but if I pull the connectors I get approx 12v to gnd on the STSW (e5-12) I cant backprobe STA (e5-11) to see what I am getting out of the ecu.
I also had less than 3v on the NSW (E6-8) in PARK, and 12v on IGSW(e3-9) with the connector unplugged.
I'm going to try to get a smaller set of probes tomorrow or find a needle or something to backprobe with.
12V on BATT(e3-3) and +BM(e3-7) I was able to backprobe these, the top row is easier maybe because the pins are larger.
+B(e3-1) and +B2(e3-2) both had 12v when backprobed with the key on.
MREL(e3-8) energizes the efi relay when the key is turned on.
I checked the ecu grounds ME01, E1, E01, E02, E03, E04, and E05 and they are all grounded.
I checked the Ignition switch contacts per the FSM and it tests good.
At some point I noticed I no longer have a check engine light on the dash. and my scan tool no longer connects to ecu. Scan tool does get power and ground, just says failed to connect after a minute or two.
Borrowed a different scan tool, same thing.
I bought a replacement ecu 89661-0C640, same exact part number, supposed to be a good one and I have the exact same symptoms. No crank, no check engine, scan tool wont connect, funny voltage to start relay coil, etc..
I pulled the gauge cluster and checked the check engine light with my meter and I think its ok (1.2v on diode scale). I can put 12v to it and see if it illuminates if needed.
So, at this point I'm not sure if my issue it still with the ecu, its funny I don't get a CEL when I turn the key on, and the scan tool wont talk to it. But I already swapped it and what would be the odds of getting one with the exact same problem? I would lean toward a wiring issue, but I don't see any problems there at all either. Nothing I have checked was shorted or open.
I see that the TVIP is also in line with the start circuit and I don't have a good way to test that. I did do the lock/unlock sequence with the fob 3 times, open door, lock unlock 3 times with switch etc to put it into passive mode and it did the answer back both times as it was supposed to.
I did ohm out the green/red wire from the TVIP to the start relay that passes through J26 and it ohms out fine.
I think some of my next steps are going to be ohm out from the DLC3 back to the ecu to see if a wire is open preventing the scan tool from working. I think I ohmed the pink wire (e5-11) from the ecu to the TVIP but I need to double check on that. I've started taking notes on what I have done but I think I checked that earlier.
If anyone has any ideas on where to go from here I would greatly appreciate it,
Tim
Here are the major troubleshooting steps I've taken:
Battery is a fairly new DieHard AGM and measures a little bit more than 12 volts. I'm using a Fluke 87, so i'm sure my readings are fairly accurate. I work as an industrial electrician in my day job.
If I pull the start relay and jump across it with a wire, the starter turns the engine fine. I think the starter is not the issue.
The start relay measured fine, but I swapped it with a spare just in case. No change, put original back.
If I pull that start relay and measure voltage across where the coil side would plug in I get about 8.5 volts in both run and start - very weird.
STA fuse is good and gets 12v to gnd when the key is turned to start.
I've checked all the fuses under the hood and under the dash.
I opened the fuse box under the hood to check for rodent damage (as in pulled from the inner fender, undid the clips and removed the bottom to look at the internal wiring). All looks good.
At this point I downloaded the FSM
I'm having trouble backprobing the ecu, but if I pull the connectors I get approx 12v to gnd on the STSW (e5-12) I cant backprobe STA (e5-11) to see what I am getting out of the ecu.
I also had less than 3v on the NSW (E6-8) in PARK, and 12v on IGSW(e3-9) with the connector unplugged.
I'm going to try to get a smaller set of probes tomorrow or find a needle or something to backprobe with.
12V on BATT(e3-3) and +BM(e3-7) I was able to backprobe these, the top row is easier maybe because the pins are larger.
+B(e3-1) and +B2(e3-2) both had 12v when backprobed with the key on.
MREL(e3-8) energizes the efi relay when the key is turned on.
I checked the ecu grounds ME01, E1, E01, E02, E03, E04, and E05 and they are all grounded.
I checked the Ignition switch contacts per the FSM and it tests good.
At some point I noticed I no longer have a check engine light on the dash. and my scan tool no longer connects to ecu. Scan tool does get power and ground, just says failed to connect after a minute or two.
Borrowed a different scan tool, same thing.
I bought a replacement ecu 89661-0C640, same exact part number, supposed to be a good one and I have the exact same symptoms. No crank, no check engine, scan tool wont connect, funny voltage to start relay coil, etc..
I pulled the gauge cluster and checked the check engine light with my meter and I think its ok (1.2v on diode scale). I can put 12v to it and see if it illuminates if needed.
So, at this point I'm not sure if my issue it still with the ecu, its funny I don't get a CEL when I turn the key on, and the scan tool wont talk to it. But I already swapped it and what would be the odds of getting one with the exact same problem? I would lean toward a wiring issue, but I don't see any problems there at all either. Nothing I have checked was shorted or open.
I see that the TVIP is also in line with the start circuit and I don't have a good way to test that. I did do the lock/unlock sequence with the fob 3 times, open door, lock unlock 3 times with switch etc to put it into passive mode and it did the answer back both times as it was supposed to.
I did ohm out the green/red wire from the TVIP to the start relay that passes through J26 and it ohms out fine.
I think some of my next steps are going to be ohm out from the DLC3 back to the ecu to see if a wire is open preventing the scan tool from working. I think I ohmed the pink wire (e5-11) from the ecu to the TVIP but I need to double check on that. I've started taking notes on what I have done but I think I checked that earlier.
If anyone has any ideas on where to go from here I would greatly appreciate it,
Tim
