Technical Efi Question On 1991 Es250

[carlfino]

I have 2 technical questions...

1. I am getting a fault code 51 ("Switch Condition") consistently after clearing the codes. The idle increases when I engage the AC, so that works. The starter will not engage when in a gear other than P or N, so I conclude that works as well. In checking the TPS the manual calls for a 5V signal being sent to the TPS via the IDL and E2 conductors. I am getting 12V, not 5V. Testing of the TPS shows that it does provide a resistance called for when at idle (2.3k ohms or less) and the resistance opens up just as the throttle opens beyond idle.

Should the voltage that the ECU is sending the TPS be 12V or 5V? Do I have a bad ECU? And does error code 51 evaluate any other switches other than Neutral start, A/C and TPS switches?

2. I am attempting to set the ignition timing by placing a jumper wire between terminals E1 and TE1. It shows about 10 BTDC for base timing, which is what the manual calls for - no problem there. However, the manual also indicates that the "Advance Timing" should be 13 - 27 BTDC, which occurs when the jumper wire is removed. When I remove the jumper wire there is absolutely no difference in the timing or the sound/rpm of the engine. Timing stays at 10 BTDC. When I put the jumper wire in the engine idle increases to about 1500 rpm for about 2 seconds then goes back to base idle (700 rpm).

Is something wrong? Shouldn't the timing advance when I remove the jumper wire? Also, could this be related to question #1 above?

Thanks to all the technogeeks that respond.

Carl...

[ArmyofOne]

I have 2 technical questions...

1. I am getting a fault code 51 ("Switch Condition") consistently after clearing the codes. The idle increases when I engage the AC, so that works. The starter will not engage when in a gear other than P or N, so I conclude that works as well. In checking the TPS the manual calls for a 5V signal being sent to the TPS via the IDL and E2 conductors. I am getting 12V, not 5V. Testing of the TPS shows that it does provide a resistance called for when at idle (2.3k ohms or less) and the resistance opens up just as the throttle opens beyond idle.

Should the voltage that the ECU is sending the TPS be 12V or 5V? Do I have a bad ECU? And does error code 51 evaluate any other switches other than Neutral start, A/C and TPS switches?

2. I am attempting to set the ignition timing by placing a jumper wire between terminals E1 and TE1. It shows about 10 BTDC for base timing, which is what the manual calls for - no problem there. However, the manual also indicates that the "Advance Timing" should be 13 - 27 BTDC, which occurs when the jumper wire is removed. When I remove the jumper wire there is absolutely no difference in the timing or the sound/rpm of the engine. Timing stays at 10 BTDC. When I put the jumper wire in the engine idle increases to about 1500 rpm for about 2 seconds then goes back to base idle (700 rpm).

Is something wrong? Shouldn't the timing advance when I remove the jumper wire? Also, could this be related to question #1 above?

Thanks to all the technogeeks that respond.

Carl...

dude, it sounds to me like your ECU is working exactly as its supposed to.

I dont knwo where you are located, but if the car is around any corrosive material (I.E., high humidity, salt etc) then the wiring connectors may have corroded on certian components...Otherwise, no...a 51 indicaes nothing other than the probems listed. pull your battery cables for 20 mins and see if the light goes away.

the OBDI system is TERRIBLY unreliable in this car, i dont knwo what it is about it, but get used ot the light being on.

The enmgine RPM doesnt change, because the ECU is compensating.

Having said that, your car has the brain of a 1990 Camry V6...which really is no brain at all. the "ECU" controls 3 things, your electrical system, your EFI, and your fuel pump. thats pretty much it bubba.

[Toysrme]

The timing is fine. The reason they give such a broad range is that the ignition timing is also varried to help stabalize the idle. The reason the engines all rev when they enter diagnostics mode is because the ECU opens the idle speed control valve (Of whatever type) to maximum open & then settles it back down. Which lets the technitian know it's not broken without having to play with it.

All main sensors on any management system I can name run off a roughly 5v, which is sourced from whatever the ECU is. (The ECU's do this because they can monitor & compensate for the small differances in the supply that would otherwise throw off all forms of sensors. TPS, MAF/AFM/MAP sensors of all kinds, etc.) The TPS in your case does run 5v from the ECU. Make sure your're checking it to ground.

It should be *close* to 0v @ idle & *about* 5v @ wide open throttle. If not, make sure the cables let it close all the way, and that the TPS sensor is in adjustment. While it comes up fairly rarely on the Lexus/Camry forums, all of the older school Toyota/Lexus TPS's are pretty bad to go out of adjustment at some time. They just don't normally cause any sort of problem that would be obviously unless you drove a good & bad one back to back.

AFA the code you pulled, nope you got it right. TPS's IDL, A/C & Neutral Start Switch.

[carlfino]

Thanks for the very helpful info.

I have not directly measured the voltage at the ECU for the IDL and E2 conductors. Rather, I pulled the connector at the TPS and measured the voltage on the connector. The 12V was measured IDL to E2 and IDL to ground (- at battery). I'll make the measurement with the connector engaged to the TPS and see what I get. If I get more than "about 0V" at idle (which I may since I have 12V being fed to it, rather than 5V), then this may be the cause of the code 51 problem, as the ECU would think the engine was not at idle. I did have to adjust the TPS to get the proper clearance between the throttle stop screw and the throttle plate tab, so this is correct.

You indicated that the voltage should be about 0V at idle and about 5V at WOT. My read is that the 5V also should be measured anytime the throttle plate is not in the idle position. Does this sound correct?

I have never looked at the ECU. I imagine that is has a 5V voltage regulator on its circuit board, which I know I could change out. The question is how accessable is the circuit board? What is the easiest way to gain access to the ECU? My manual states that it's somewhere behind the dash. Can you be more specific as to its location and how to access it?

Thanks Toys,

Carl...

[Toysrme]

My words of stupidity are, "Never touch a Toyota/Lexus/Scion ECU. I've never seen one fail unless the user did it".

It's like this. The ECU supplys the AFM & TPS with roughly 5v (VC). (Just so it always knows what the starting voltage is regardless of the system.)

The TPS is just a pot. The plate spins the pot & the resisitance changes -> the voltage the ECU sees coming back from the pot changes (VTA signal). Now if it stopped there, they'd go out of calibration all the time. What Toyota did was take & add another output (IDL) to it where if the swing arm is in the general range of an idle / closed throttle. It sends a signal to the ECU. The ECU takes that signal & basically uses it as a starting point for throttle position.

If you check the VTA signal while the car is just turned ON (not running). It shoul start at 0v & swing up to around 5v. It won't be exactly that, just as long as it starts at next 2 nothing & goes pretty close to 5v you're fine. The IDL voltage should trip quickly if you open the throttle.