Troubleshooting AKA what's wrong with my car

This is an ongoing work to include common things to check yourself (or telling you you can't). Questions, comments, suggestions: let me know and I'll try to include them. This thread is closed for the sake of cleanliness.

*Yes, it would be easier to just post the TSRM but copyright stuff doesn't allow it so don't ask. If you have it or want it, use the private message system.*
There is a set online for the USDM Supras that is very useful. You can navigate there by going to www.cygnusx1.net click supra, then tech tips, then pick either the MK2 (for 5MGE) or MK3 (7MGE/GTE) TSRM. for 95% of the engine and transmission, it's the same. Suspension for all practical purposes is the same on the X7/MK2, rear is very similar for the X8/MK3 but front is very similar to the MK2/x7. Wiring and body, obviously, will be different. Many other things carry over but I haven't done enough cross checking to explain exactly what does or does not transfer.

Trouble codes
Whenever it runs anything but perfect, the first thing to do is check for stored codes. This is just asking the computer if it thinks anything is wrong, depending on what it says affects where you go afterwards. USUALLY the check engine light will be on if there's a code. Sometimes it isn't though so check ust in case.The nice thing about Toyota back in the day is that they provided a means to do so without any fancy tools. All you need is a few inches of wire with the ends stripped. For the MX73 (and MX72) the diagnostics connector is between the fuse box, coil/ignition module, and injector resister.
https://2img.net/h/i29.photobucket.com/albums/c265/kamesama980/88%20Cressida/DSCF0637.jpg
The MX83 diagnostic connector is located on the strut tower next to the intake manifold, just forward of the brake master cylinder. MX63 is similar but I've never had to work on one so I don't have pix. Someone help me out here?

When you open it up, there should be a label inside the cap saying which pin is what (as soon as I find a pic, I'll link to it here).

FOR THE ENGINE: The pins we're looking for are TE1 and E1. Stick the wire into the plug at those pins (make sure stray strands don't go elsewhere). Once it's in, go inside the car and turn the key on without starting the car (KOEO or key on engine off). the check engine light will flash indicating what the computer thinks is the problem. each group of flashes corresponds to a number, each code is made up of two numbers. Each code will repeat 3 times before moving on. when all the codes have been displayed, they will repeat from the beginning.

The following conditions must be met before the ECU will display codes:
-Battery voltage above 11 volts
-Throttle valve fully closed (IDL switch closed)
-Transmission in P or N
-AC switch off (on the heater controls)
-Engine at normal operating temp (I've pulled codes many times with a cold engine, so maybe not?)

Some of the codes list chassis numbers, that means that that code is only for the listed number according to the documentation I have.

Anyway, the codes are as follows:
-steady on/off every 1/4 second: everything OK
-11: ECU B+ interrupted
-12: RPM signal: no NE, G signal to ECU within weveral seconds after engine is cranked
-13: RPM signal: no NE signal to ECU within several seconds after the engine reaches 1k rpm
-14: ignition signal: no signal from igniter six times in succession
-16: (MX83) ECT control signal (ECT control program: faulty ECU)
-21: Oxygen sensor signal; sustained lean (usually the O2 sensor isn't the root problem, usually something else is causing a problem that is manifested here.)
-22: water temp sensor signal (open or short)
-23: (MX63/73) Intake air temp sensor signal (open or short)
-24: (MX83) Intake air temp sensor signal (open or short)
-25: (MX83) A/F ratio: lean
-26: (MX83) A/F ratio: rich
-27: (MX83 CA) Sub-O2 sensor (post-cat) (open or short in sensor circuit or heater circuit)
-31: Air flow meter signal (open in Vc or Vs and E2 shorted when TPS IDL circuit closed)
-32: Air flow meter signal (open circuit in E2 or Vc and Vs short circuited)
-34: (MA70/7MGTE) Turbocharger pressure abnormal
-35: (MA70/7MGTE) HAC signal (open or short)
-41: Throttle position sensor (open or short in TPS signal)
-42: Vehicle speed sensor (VSS tells ECU under 2kmh with 2500+ rpm for 5 seconds. IF A/T: range selector not in P or N)
-43: starter signal (no STA signal to ECU when engine is running over 800 rpm)
-51: NSS off or AC switch on during diagnostic check
-52: knock sensor (open or short)
-53: knock sensor signal (faulty ECU)
-71: (MX83 CA) EGR system (gas temp sensor reads low, open circuit in EGR GTS)


FOR THE TRANSMISSION:
MX73 and MX83: The pins we're looking for are Tt and E1. Again, stick the wire in to short these pins.
MA60: short pin Dg to ground
MX63: probably short pin Dg to ground (can anyone verify?)
Make sure the OD button is pushed in (so that overdrive is active and the light is normally off) and turn the key on without starting the engine. Same deal as the check engine light with the blinks but the "OD off" light will be blinking instead of the CEL

The TCU does not have any prerequisites to display codes according to the TSRM except that the OD button must be ON (pushed in) or the light will be lit steady.

-42: Defective no. 1 speed sensor (in combination meter (gauge cluster)) - severed wire or short circuit
-61: Defective no. 2 speed sensor (in transmission) - severed wire harness or short circuit
-62: #1 Solenoid - severed wire or short circuit
-63: #2 Solenoid - severed wire or short circuit
-64: lock-up Solenoid - severed wire or short circuit


OIL LIGHT:
the factory oil warning light is set to come on if the oil pressure drops below about 3 psi. the spec for pressure at idle is 4 psi. that means if ANYTHING isn't perfect, the light will be on and you'll probably still be fine. the switch for the light is also prone to getting tired with old age and coming on inappropriately. replacing the switch has fixed the problem many times. (there are many reports of aftermarket switches that turn on at different pressures, Toyota ones tend to be more consistent (and correct)

If the light is on dim at idle and gets brighter as the engine is revved up, you have a supra variable sending unit for the oil gauge installed instead of the switch. No you can't make it work short of using a supra gauge with it. unplug it, install the cressida on/off oil light switch, or get an aftermarket gauge if you care at all.

BRAKE LIGHT:
can be turned on 4 ways in most models. If it's on, it's one of these. Onve you figure out which you can move to troubleshooting that system.
-low fluid. There's aswitch on the master cylinder cap attatched to a float. When the float gets low enough, the switch closes and the light comes on.
-Hand brake is on. There's a switch on the emergency/parking/hand brake lever. when it isn't all the way down, the switch closes and turns the light on.
-in conjunction with the battery and 'lights' light as a message to say the computer has noticed a problem with the alternator with how it's charging that wouldn't turn on the battery light.
-something broke. Failed switch, shorted wire, etc.

BATTERY LIGHT
It's turned on when the alternator output falls below the battery voltage. basically one side is hooked to B+ and the other to the alternator +. as long as you've got + voltage on both sides, the light stays off. If the alternator stops charging altogether, the light grounds through the alternator and turns on. Kinda counterintuitive but that's how it works.
-If it comeson with the brake and 'lights' light, then you also have alternator failure but not quite the same way.

LIGHTS LIGHT (looks like the back of the car with a few lines coming off of it)
-Check your taillights, one's probably burnt out.
-This one can also turn on if the light-out detection module is damaged. it's a little bright colored box in the trunk under the liner. leaky trunk seals are the #1 killer: the water or even humidity causes corrosion on the circuit board.

Reserved for future use

reserved for future use