Background: 2000 Odyssey with 189K miles, american car. Transmission just rebuilt, driving for the first time - TCS light stayed on after starting.
Pulled the codes, codes 34 and 31 came up - TCS codes, not to be confused with ABS codes.
The codes are indicated as low reference voltage and permissive missing respectively.
I backprobed the relevant connectors and found 5V reference from the ECU to the TCS unit... at the time the car wasn't able to run due to a drained battery, so I didn't troubleshoot code 31 at that time. I reset the codes. Car is running now with a new battery so I went back to troubleshoot code 31, I started the car and the TCS light came on several seconds after starting the car. I backprobed the relevant permissive pin with an analog meter. Nothing there. It was wicked cold out so I didn't carry on with getting the ECU pulled and checking the permissive signal at the ECU itself. I wanted to do more research about the subject. The troubleshooting at this point says to replace the ECU. Seems a little excessive, and I wonder what the actual permissive signal from the ECU consists of? One has to assume that the ECU is looking for conditions to be met in order to give the signal to the ABS/TCS unit. So if I'm missing a condition, seems ridiculous to go and replace an ECU that is doing what it's supposed to. I should point out, this time only code 31 was set. I suspect code 34 was set when I was cranking the car with an almost dead battery, voltage prob dropped below the threshold necessary and the code was set. I'm no longer worried about that code.
In summary, the question is:
What makes up the permissive signal from the ECU to the TCS; ie. what conditions cause that signal to be withdrawn?
If there weren't any conditions, then one would assume that TCS would just be wired to run anytime the engine was running and the vehicle was not in Park or Neutral. However, this is a heartbeat signal, as in, a pretty robust 'permission' communication method as far as controls goes. The heartbeat is 50% duty cycle between 0 and 5V, meaning a square wave (at an unknown-to-me) frequency. All I know is an analog meter should show the signal as a 2.5V reading according to the service manual. Neither the service manual nor the electrical troubleshooting manual offer any further insight, presumably discussion of controls logic is beyond the scope of a shop manual.
Pulled the codes, codes 34 and 31 came up - TCS codes, not to be confused with ABS codes.
The codes are indicated as low reference voltage and permissive missing respectively.
I backprobed the relevant connectors and found 5V reference from the ECU to the TCS unit... at the time the car wasn't able to run due to a drained battery, so I didn't troubleshoot code 31 at that time. I reset the codes. Car is running now with a new battery so I went back to troubleshoot code 31, I started the car and the TCS light came on several seconds after starting the car. I backprobed the relevant permissive pin with an analog meter. Nothing there. It was wicked cold out so I didn't carry on with getting the ECU pulled and checking the permissive signal at the ECU itself. I wanted to do more research about the subject. The troubleshooting at this point says to replace the ECU. Seems a little excessive, and I wonder what the actual permissive signal from the ECU consists of? One has to assume that the ECU is looking for conditions to be met in order to give the signal to the ABS/TCS unit. So if I'm missing a condition, seems ridiculous to go and replace an ECU that is doing what it's supposed to. I should point out, this time only code 31 was set. I suspect code 34 was set when I was cranking the car with an almost dead battery, voltage prob dropped below the threshold necessary and the code was set. I'm no longer worried about that code.
In summary, the question is:
What makes up the permissive signal from the ECU to the TCS; ie. what conditions cause that signal to be withdrawn?
If there weren't any conditions, then one would assume that TCS would just be wired to run anytime the engine was running and the vehicle was not in Park or Neutral. However, this is a heartbeat signal, as in, a pretty robust 'permission' communication method as far as controls goes. The heartbeat is 50% duty cycle between 0 and 5V, meaning a square wave (at an unknown-to-me) frequency. All I know is an analog meter should show the signal as a 2.5V reading according to the service manual. Neither the service manual nor the electrical troubleshooting manual offer any further insight, presumably discussion of controls logic is beyond the scope of a shop manual.
