Flymase

08 Lexus GS350. Drove car Christmas Eve everything was fine, Christmas morning I go to start the car and it attempts to start once and before it cuts on it stops. Then anytime afterwards when I push the start button the starter doesn't engage and the radiator cooling fan comes on. I let the car sit for half a day and try to start it again I get the same cycle ( it engages the starter but quits before the car turns over)
- Battery is new as of September 14 (also took the battery to get checked 100% charged).
- I replaced the alternator in November 14
- I currently have the car at my mechanics but they can't figure it out as of yet. So far they are saying that the can't the cars computer to respond to their machine.

Any help would be appreciated. Thanks!

Gotcha350

Starter? Or possible shift lock problem? Just taking a guess but you did say it just stop trying to crank right in the middle of you starting it.

Flymase

Yep, after the car sits a while I can press start and the starter engages but before the engine turns all the over it just stops. The shop is still testing but are thinking ecu. They still dont know

Gotcha350

So that eliminated the shift lock issue...still could be a starter issue...dont see how the ECM would let the started engage but not allow it to even try to turn the engine over...

Flymase

Me either but who knows with these cars. My power steering went out when the alternator failed. Technology has changed so much that you can't just pinpoint failed parts like the old days.

jbounds

mine did the exact same thing this morning!!! how nuts! My mechanic is simply scratching his head.

jbounds

any update?

baldrick

The ECU will let go of the starter relay even during a crank if it detects any electrical issue with the relay. The ECU is not directly connected to the starter since it cannot source the high current. It doesn't take much current to control the starter relay compared to the starter itself.

if your mechanic does not have a Lexus or Toyota diagnostic tool, and the wiring diagram for the vehicle, they are wasting their time and yours. The tool can command the starter relay ON by sending a message to the ECU directly without anyone pushing the start button. The ECU has to interpret the received message and then act on it. it's the way we design ECU functionality, and one sure way to tell if the ECU is working properly.

Gotcha350

Nice info Baldrick! Thanks for that write up.

burny

ole Bald Rick is the man

jbounds

not sure I understand Baldricks message, am I to assume the ecu is bad?

Flymase

Good info, I'll relay it to my mechanic. No update as of today. They told me today that when they unhooked the ecu the cel comes on. They also said the cooling fan is running all the time (this didn't start until this issue started). They are scratching their heads because the ecu won't respond to their tool at all.

chuckGS350

Maybe the coolant temperature sensor goes bad.

Flymase

They are going to have to get my car starting first before The diagnose my cooling fan issue. The cooling fan wasn't an issue until the car stopped starting.

baldrick

They have to go to the TIS website (Toyota Information Services) and buy a 2-day subscription for $15. this gives them access to wiring diagrams for every single electrical component in the vehicle. they can also download troubleshooting guidelines for a boat load of problems.

For 2008, it is likely CAN protocol is used for communication between a test tool and the numerous electronic modules in the vehicle. If their tool does not support CAN, it cannot talk to anything on the vehicle. secondly, if the tool supports CAN but the 2 wires which make up the CAN backbone is cut or missing either of the 120-ohm resistors, no talk. No messages from the tool will get through to the ECU.

thirdly, some vehicles need a "bridging" wire across 2 pins before a ECU will communicate with a test tool. This setup was on the older vehicles, last time I saw this was on a 2002 or 2003 model year vehicle.

The push button, vehicle security system, key fob and brake pedal information are shared among all modules on the CAN link. the fact that you get cranking after pressing the push button seems to indicate the communication lines are intact, especially since only the ECU controls the starter relay (unless you have remote start, then all bets are off about who controls that).

the fan running all the time indicates a short circuit of the fan. There is a separate fan control module which attaches to the fans. This module gets its instructions from the ECU, based on what the oil or coolant temperature sensor reports. the 2nd fan is told to run when the a/c is commanded on. if these sensors mistakenly read hot when the oil or coolant are cold, the fan will run. The temperatures are expected to drop as the fan runs (feedback controls), if not something isn't right and ECU will turn your CEL on and set a "plausibility or performance" fault. however a shorted fan is a run away horse, no control. eventually the fan will fail. the cooling fan should only run with engine ON and a few other conditions. it should shut off when engine is turned off. a constantly running fan with engine not running is exactly what a short-circuited fan will do. until the battery runs out of juice...

cutting a long story short, without the wiring diagram, they have no chance figuring out wtf is going on. If I were your mechanic, I would pay the $15 and start downloading. and find someone who knows how to use a multimeter and read schematics.

It does not necessarily mean a bad ECU at this point. they need to backtrack from the fan, and starter circuits with the help of the diagrams. There is also information on how to diagnose a bad ECU, and what to do when it will not communicate. Like I said earlier, the tool must support CAN. the old J1850 protocol will not work on a 2008 Lexus, and some tools are known to not switch to different protocols when J1850 does not work.