Valet Mode How-to

Last updated: February 27, 1999

Date: Sun, 21 Feb 1999 19:18:15 -0500
From: "Houseman, Carl W. x1323"

>... a lost memory about posts discussing the installation of a switch to
> activate the "limp home" mode.    I'd like to add such a switch to activate the
> limp- home mode whenever I leave my car anywhere.   What circuit must be
> interrupted to activate the limp-home mode?

I wrote the posts in the past about doing this... Those posts got to be a little long (in two parts) so here is the one-post abbreviated version.

Basically at the ECU you want to short the double-throttle solenoid output to ground, which keeps the DT closed, and open-circuit the wastegate solenoid output, which puts the wastegate in fail-safe 7 PSI mode. This results in reduced first-turbo performance and a rev limit at about 5500 RPM with no ill effects that I could see.


DT solenoid wire is Black/Red wire on the end of the smallest ECU connector. Use a 2-pole switch which changes the circuit as follows:
Pole #1: disconnect the wire from the ECU and connect it to ground.
Pole #2: connect a 1K resistor between ground and the ECU lead.

This is being overly cautious as I would prefer not to directly ground out the circuit while the lead is connected to the ECU. I imagine the ECU can handle this but I wouldn't do it.

WG solenoid wire is the Blue/White wire on the largest ECU connector. Simply break the circuit with the switch.

To do all of this with the flip of ONE switch would mean you're looking for a 3PDT switch.

This will give you two codes in your ECU. After un-setting limp-mode, you should erase the codes from the ECU (step on brake pedal with battery disconnected).

Make these mods at your own risk, and as always I recommend that anyone doing electrical mods have the wiring diagrams to refer to. My reference is the 94 wiring diagrams.

Of course, even so disabled the car is pretty peppy, but it should be harder to get up to 70 mph in a parking lot. A PARKING LOT! I still can't believe it. This is really a case for a 20/20 hidden camera investigation. "What do they do with your car while you're not there". Not all that different from "what does the baby sitter do with your kid while you're away".


From: Carl Houseman
Date: June 18, 1995

Valet parking switch - project report, 1997-05-18

Well, I now have a pushbutton in the glovebox door jamb that electronically cripples my car in the same ways that some of you have reported from other causes :-). Details:

I chose to disable the double-throttle control and wastegate outputs from the ECU. The wastegate output was easy... just open the circuit to disable it. However, the ECU would normally be offended at the disconnected wire, so instead of a true open circuit, my switch inserts a 1K resistor in series with the wastegate solenoid, which reduces the current so that the solenoid doesn't operate.

On the double-throttle control, I was going to do the exact same thing, but when it was all wired up, it didn't work. Huh? Did I get the wrong ECU lead? Nope, the 95 Service Manual LIED TO ME. It says on page F-210 that "if the circuit is open, the double throttle valve will be always closed, causing poor acceleration and lack of power." WRONG. The circuit must be grounded in order to close the double throttle valve. This complicated the wiring for this part of the switch. I ended up using another pole of my switch to ground the lead in valet mode, while a 1K pull-up resistor fools the ECU into thinking the solenoid is still connected.

Performance results... with only the wastegate output disabled, sure enough, 1st turbo topped out at about 8 PSI, and when the 2nd turbo came online it only recovered to about 6 PSI. Performance was still quite good - a first timer might think everything was fine.

Once I got the double-throttle valve to stay closed, the performance on WOT took a noticeable hit. About 5K rpm & up, it was the 3K hesitation all over again, except that there was no recovery. It would try to go faster, then falter, then go, falter, go, falter, etc. It was unnerving enough that I was unwilling to keep pressing to see what would happen above 5500 rpm. I checked for ECU error codes and there aren't any stored (and no check-engine light of course).

I'd appreciate any comments on the over-5K rpm behavior. At least the restricted airflow should not be causing a lean condition. The normal situation for the double-throttle valve being closed is a cold engine... so maybe this is the way it's supposed to act when you give WOT to a cold engine? (BTW, WRT the temp gauge behavior... my gauge indicates normal operating temp for several minutes before the ECU opens the double-throttle valve, which happens at about 176 F).

I chose not to disable the turbo control solenoids - which would keep the 2nd turbo from ever getting the full exhaust flow. Would that be a good idea given the hesitation I'm seeing above 5K?

If you want to do this yourself... it will be a week or more before I have time to prepare a decent schematic... and I'm not sure I want to recommend this mod to anyone, unless somebody can convince me the that the 5K hesitation is no concern.

[ Mail me ] [ To Lightning home page ] [ To my home page ] [ Copyright Notice ]