ECU will not Communicate - Troubleshooting Assistance - Lexus IS Forum
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post #1 of 13 (permalink) Old 03-24-2014, 03:55 PM Thread Starter
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ECU will not Communicate - Troubleshooting Assistance

I have a friend's '02 IS300 giving us a hard time, and at the point where now I think it's worth it to ask the guru's on here on where I should look next.

To start, my friend had her TB assembly replaced due to some code (don't know the code) from the dealership. The symptoms at the time were what I've read as a bad TPS - basically the gas pedal not responding at times, idling horribly, and at times the engine dying completely. Once this was replaced, the issue seemed to be resolved until about 150 miles, the same issues occurred. This time around, the Lexus tech's couldn't pull codes due to the ECU not being able to communicate with the scanner. After looking at the ECU, they said they wouldn't touch it until the SAFC2 was removed. Go figure right? This is where I enter. I figured out the SAFC somehow lost it's tune and was reset back to factory settings, but to be safe, I went ahead and removed it, considering how much our cars love piggybacks, and how this car is n/a.

We have the same result, the ECU cannot communicate with my scanner. The car drives fine for about 100-250 miles, and then this issue comes back again. I can't provide details on which lights on the dash are on, but for certain there's a check engine and trac off flashing when this happens, however I'm told it's NOT in limp mode, as she can rev past 3k.

My main question at the moment, is where should I start to diagnose the ECU not being able to communicate with the scan tool? At this point I've:

- Verified that the SAFC is 100% disconnected from the system. I verified that both grounds that the SAFC spliced into had solid connections, as I read somewhere that bad grounds in the ECU can 'cause it to go somewhat haywire

- Verified both Radio No. 1 and 2 fuses were good, as I also read that one of these may be the primary power source for the OBD2 link

The car does have a complete after market stereo system (nothing is stock) installed by the previous owner, but I shouldn't imagine this would impact the ECU being able to communicate with a scanner. I also realize that it was after Lexus installed the new Throttle Body that they could no longer pull codes, but again what would they do in that area that could affect the ECU being able to communicate?

After pulling the negative wire and pumping the brake pedal a few times for a hard reset, the car runs absolutely beautiful. Pulls very strong, idles great, and sometimes smells like an exhaust leak (it does have 02 sims for the headers)

If you've gotten this far, I definitely appreciate the time taken. If you have any ideas, please let me know. I've got some of my own, but I'd like to hear from some folks who have some more experience with an ECU not being able to communicate with a scanner. Thanks all

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post #2 of 13 (permalink) Old 03-24-2014, 04:34 PM
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So does the car currently run fine, cluster acts like normal? First thing I would check for a communication loss is to make sure you have B+, ground and ecu ground as shown below at the obd2 port.


I've helped members through similar experiences but usually the car won't run because either the immobilizer won't let it start or there is a ground on the 5vdc output the ECU puts out, which prevents the ECU from powering up. Bad grounds can also be a problem but not always because the grounding in this car is pretty redundant. A signal loss between the ecu and dlc3 port would cause a loss of signal/communication but the car would run fine. So this is just a comms loss at the dlc3?

'02 IS300 MSM LSD
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post #3 of 13 (permalink) Old 03-24-2014, 06:21 PM Thread Starter
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Quote:
Originally Posted by jasonm4 View Post
So does the car currently run fine, cluster acts like normal? First thing I would check for a communication loss is to make sure you have B+, ground and ecu ground as shown below at the obd2 port.


I've helped members through similar experiences but usually the car won't run because either the immobilizer won't let it start or there is a ground on the 5vdc output the ECU puts out, which prevents the ECU from powering up. Bad grounds can also be a problem but not always because the grounding in this car is pretty redundant. A signal loss between the ecu and dlc3 port would cause a loss of signal/communication but the car would run fine. So this is just a comms loss at the dlc3?
Just the man I was hoping to see a reply from! You are correct, the car currently runs perfectly fine, with the dash acting normally with the exception of an ABS light on, but that was already present. The only thing we're seeing is the loss of communication with the dlc3. I will verify the connections you specified above either this evening or tomorrow and post my results. Your expertise is always appreciated Jason!

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post #4 of 13 (permalink) Old 03-24-2014, 06:35 PM
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No problem man, I have a feeling your ECU is ok and if there is any problem at all, it may be the wiring to/from the port which I can elaborate where, the port itself or the scanner unless you've rules that out. But if the scanner isn't even turning on, I'd definitely check for power as mentioned, comes right off the 7.5A OBD fuse in the kick panel and is "hot" when the ignition is turned on as if you would be using the scanner. Most require that +12 to operate from the car or even turn on. Good luck..

'02 IS300 MSM LSD
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post #5 of 13 (permalink) Old 03-26-2014, 09:26 AM Thread Starter
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Quote:
Originally Posted by jasonm4 View Post
No problem man, I have a feeling your ECU is ok and if there is any problem at all, it may be the wiring to/from the port which I can elaborate where, the port itself or the scanner unless you've rules that out. But if the scanner isn't even turning on, I'd definitely check for power as mentioned, comes right off the 7.5A OBD fuse in the kick panel and is "hot" when the ignition is turned on as if you would be using the scanner. Most require that +12 to operate from the car or even turn on. Good luck..
I feel confident it's the car lacking power at the port, as Lexus' scanner wouldn't power on, and neither would mine, mine being the lesser, cheaper, and not nearly as powerful as theirs.

Just to verify, I did not see a 7.5A OBD fuse in the kick panel on the driver sid;, the only 7.5A fuse I saw was labeled 'starter' I believe. Is this what you were talking about, or am I just blind? This was just me checking on my own car, I haven't had time to look at my friend's car these past few days. And oddly enough, the car hit 250 miles since it's last hard ECU reset this morning, and has been driving great.

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post #6 of 13 (permalink) Old 03-26-2014, 09:33 AM
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Originally Posted by jimboozy View Post
I feel confident it's the car lacking power at the port, as Lexus' scanner wouldn't power on, and neither would mine, mine being the lesser, cheaper, and not nearly as powerful as theirs.

Just to verify, I did not see a 7.5A OBD fuse in the kick panel on the driver sid;, the only 7.5A fuse I saw was labeled 'starter' I believe. Is this what you were talking about, or am I just blind? This was just me checking on my own car, I haven't had time to look at my friend's car these past few days. And oddly enough, the car hit 250 miles since it's last hard ECU reset this morning, and has been driving great.

There should be a 7.5A OBD fuse slot on the bottom left side on the passenger side kick panel fuse box. Power comes directly off that fuse for the port, so you don't have any OBD fuse slots on either side?
A violet colored wire should come straight off the load side of that fuse and go directly to the dlc3 port(comes from harness connector 2E pin 6. Download the DI book and it will show you exactly where that is, or PM me and I'll shoot you a link.

'02 IS300 MSM LSD

Last edited by jasonm4; 03-26-2014 at 09:39 AM.
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post #7 of 13 (permalink) Old 03-30-2014, 07:40 PM Thread Starter
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Quote:
Originally Posted by jasonm4 View Post
There should be a 7.5A OBD fuse slot on the bottom left side on the passenger side kick panel fuse box. Power comes directly off that fuse for the port, so you don't have any OBD fuse slots on either side?
A violet colored wire should come straight off the load side of that fuse and go directly to the dlc3 port(comes from harness connector 2E pin 6. Download the DI book and it will show you exactly where that is, or PM me and I'll shoot you a link.
Thanks a million Jason! I looked in the driver side kick panel fuse box, thinking the fuse would be there. Sure enough, the OBD fuse was blown in the passenger side kick panel fuse box. Replaced it with a good one, and sure enough, my OBD scanner connected right up!

On the actual issue, the car went 467 miles this time before acting up. Basically it feels like the top 75% of the gas pedal doesn't actually do anything. Once you get the pedal right past that, then you get response. Sounds like either the electronic part or the manual part of the TB isn't working correctly? I'm probably off there hehe. Since I was on my way to work that morning I didn't troubleshoot, just pulled the negative off the battery for a hard reset to clear it to get to work. Regardless, now that we've got communication, next time it trips I'll be able to pull the code and start from there.

Again, can't express my appreciation enough for the knowledge and help you always bring to the table.

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post #8 of 13 (permalink) Old 03-30-2014, 08:19 PM
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Good to know and glad to hear that worked!

The last portion of the throttle is mechanical with the first ~60% controlled by the throttle wheel(accelerator pedal position sensor) which turns the throttle position motor and sensor. The last bit is all cable and sensed by both the accelerator pedal position sensor amd throttle position sensor. They both have redundant outputs which should throw a code if the specs are off(I have both posted), which are safety circuits to monitor. I would however make sure your throttle wheel turns the butterfly to the max(64%-96%) position when you have the gas pedal pushed. Normally it doesn't need adjusted from the factory and slight slack is needed or you will break the cable over time when flooring it out.

Glad I could offer some help. I have all the specs posted lemme know if you can't find them. I would think if either sensor is even slightly off it will throw a code soon. Good luck, let us know.

'02 IS300 MSM LSD

Last edited by jasonm4; 03-31-2014 at 03:39 AM.
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post #9 of 13 (permalink) Old 03-31-2014, 01:48 PM
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Connect your scanner and make sure the TPS Voltage is set to about 14.5 or so. If it is above 15 or below 14, the TPS will disengage while you are driving and it will not turn back on until you turn off the car and turn it back on.

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post #10 of 13 (permalink) Old 09-20-2016, 03:12 PM
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can anyone help my 2003 lexus Es300 stop working one day it will crank and will not start the security light blinks and also i am unable to communicate with the ECM when i hook up a scan tool to the obd port
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post #11 of 13 (permalink) Old 02-27-2017, 07:21 PM
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I currently do not have any warning lights but have invested in a scanning tool for my IS300, the second I plug it in it powers up but when going though its connection protocols it doesn't connect to any and throws a message on the tool unable to establish link, I have tested the tool on my wife's car and it works fine her car is a GM, so assumed the error was due to the tool being a cheap eBay one. I have now invested in a more expensive tool which supports all vehicles from 96-16
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Wires are good..still no communication with mine
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post #13 of 13 (permalink) Old 08-10-2018, 12:43 PM
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So guys I'm bringing this thread back up. I have the same issue with communication with the ecu. regarding the 5vdc to the power the ecu. the 7.5 amp fuse on the passenger kick panel is good and all fuses have been checked and confirmed good. any help tips would help me start testing further
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