The always frightening electrical problems

supraheelfan · 01-24-2012, 10:59 PM

no previous thread just wanted whoever replies to know what I'm dealing with. Error codes 12, 21, and 24. I've looked for vacuum leaks (no leaks) but haven't checked AFM yet.

cre · 01-25-2012, 05:11 AM

So codes for: CPS or ECU, Oxygen sensor or ECU and AFM temp sensor or ECU.....

The code 12 may be set if the vehicle stalls and is restarted by 'popping the clutch' or if it is push started. So if you've done either recently you may want to clear the codes and see if this one returns. If it does a bad CPS, wiring, fault in the starter circuit or the ECU may be to blame.

The code 21 well, a bad oxygen sensor won't cause a significant change in the fueling. The ECU is SUPPOSED to disregard the OX input after a minute or so of an 'out of bounds' signal. You may disconnect the O2 sensor to put the car into open loop operation to see if it drives any better.... BUT even if it does drive better that doesn't mean the O2 sensor was to blame.

Code 24 is important. The ECU must know what temperature the incoming air is in order to properly adjust timing and fuel. Test the AFM before anything else.

supraheelfan · 01-26-2012, 12:19 AM

If I clear the error codes would I have to drive the car again for the codes to show back up?

cre · 01-26-2012, 12:33 AM

I already answered that. To clarify: Some will show up at the ECU power up diagnostic; Some will appear when you run the car for a couple minutes (just idling will do); Some require the engine to be up to normal operating temp and running; And some require you to drive the vehicle to give it a chance to sample data at various load levels.

supraheelfan · 02-13-2012, 09:53 PM

I have a question: A mechanic I just recently met said since I have a used JDM engine and the original ECU wiring harness from the old 7mgte, that I need to "upgrade" by getting some new sensors so the ECU can read the signals it needs to operate the engine. Is any of this true? He wouldn't clarify which sensors he was talking about and he said there is about 3 sensor that needed to be upgraded..

cre · 02-13-2012, 10:03 PM

The ONLY sensor which isn't cross compatible is the oil pressure sensor. If it's a California car (originally sold in Cali) the ECU will also be expecting signal from a sensor in the EGR cooler which other MKIIIs don't have; As you don't have an error code for that sensor I assume that to not be a Cali vehicle or the swap was more complete.

Does your oil pressure gauge work?

How does he know it's JDM? It's not written anywhere and aside from the oil pressure sender and the way the coolant is routed there are no other differences.

cre · 02-13-2012, 10:51 PM

I suppose it is worth mentioning that there were a number of changes made to the electrical system throughout the '89 model year. Pretty much all of the components are cross compatible but most have different plugs, the wire harness changed, the external HAC sensor was built into the ECU, the ECUs are different (many different models actually but the only significant difference it the redline depending on wether the engine has a 6M or 7M crank). The AFM and TPS connectors are the same as are all of the temp sensors and the oil pressure sender, the CPS is different and you wouldn't be able to plug it in and the wrong TPS will plug in but the interface tabe will be clocked 90? differently than the tabs on the throttlebody. The significant differences in ECU are highlighted by the harness connector colors.... Basically, if plugs and connectors are yellow it'll work and if they're both grey it'll work.

Again, it doesn't sound like any of this is the case with your vehicle.

01-25-2012, 05:11 AM	#2
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	So codes for: CPS or ECU, Oxygen sensor or ECU and AFM temp sensor or ECU..... The code 12 may be set if the vehicle stalls and is restarted by 'popping the clutch' or if it is push started. So if you've done either recently you may want to clear the codes and see if this one returns. If it does a bad CPS, wiring, fault in the starter circuit or the ECU may be to blame. The code 21 well, a bad oxygen sensor won't cause a significant change in the fueling. The ECU is SUPPOSED to disregard the OX input after a minute or so of an 'out of bounds' signal. You may disconnect the O2 sensor to put the car into open loop operation to see if it drives any better.... BUT even if it does drive better that doesn't mean the O2 sensor was to blame. Code 24 is important. The ECU must know what temperature the incoming air is in order to properly adjust timing and fuel. Test the AFM before anything else. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

01-26-2012, 12:33 AM	#4
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	I already answered that. To clarify: Some will show up at the ECU power up diagnostic; Some will appear when you run the car for a couple minutes (just idling will do); Some require the engine to be up to normal operating temp and running; And some require you to drive the vehicle to give it a chance to sample data at various load levels. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

02-13-2012, 10:03 PM	#6
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	The ONLY sensor which isn't cross compatible is the oil pressure sensor. If it's a California car (originally sold in Cali) the ECU will also be expecting signal from a sensor in the EGR cooler which other MKIIIs don't have; As you don't have an error code for that sensor I assume that to not be a Cali vehicle or the swap was more complete. Does your oil pressure gauge work? How does he know it's JDM? It's not written anywhere and aside from the oil pressure sender and the way the coolant is routed there are no other differences. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

02-13-2012, 10:51 PM	#7
cre Toyota Racing Development Join Date: Apr 2007 Posts: 5,038	I suppose it is worth mentioning that there were a number of changes made to the electrical system throughout the '89 model year. Pretty much all of the components are cross compatible but most have different plugs, the wire harness changed, the external HAC sensor was built into the ECU, the ECUs are different (many different models actually but the only significant difference it the redline depending on wether the engine has a 6M or 7M crank). The AFM and TPS connectors are the same as are all of the temp sensors and the oil pressure sender, the CPS is different and you wouldn't be able to plug it in and the wrong TPS will plug in but the interface tabe will be clocked 90? differently than the tabs on the throttlebody. The significant differences in ECU are highlighted by the harness connector colors.... Basically, if plugs and connectors are yellow it'll work and if they're both grey it'll work. Again, it doesn't sound like any of this is the case with your vehicle. __________________ If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum. If you're so inclined I'm always more than happy to accept tips via PayPal. Tip Jar --->

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01-24-2012, 10:59 PM	#1
supraheelfan 3" Exhaust Join Date: Feb 2011 Location: Wilmington, NC Posts: 178	no previous thread just wanted whoever replies to know what I'm dealing with. Error codes 12, 21, and 24. I've looked for vacuum leaks (no leaks) but haven't checked AFM yet.

01-26-2012, 12:19 AM	#3
supraheelfan 3" Exhaust Join Date: Feb 2011 Location: Wilmington, NC Posts: 178	If I clear the error codes would I have to drive the car again for the codes to show back up?

02-13-2012, 09:53 PM	#5
supraheelfan 3" Exhaust Join Date: Feb 2011 Location: Wilmington, NC Posts: 178	I have a question: A mechanic I just recently met said since I have a used JDM engine and the original ECU wiring harness from the old 7mgte, that I need to "upgrade" by getting some new sensors so the ECU can read the signals it needs to operate the engine. Is any of this true? He wouldn't clarify which sensors he was talking about and he said there is about 3 sensor that needed to be upgraded..