1993 does not have a temp sensor but is throwing a 71 sensor code (1 Viewer)

Traakon

SILVER Star
Joined
Mar 22, 2015
Messages
258
Location
Queen Creek, Az.
OK, I have been reading on this topic for the entire time I have owned the '93 "Cruiser".

All of the components in the EGR system have been replaced and intake cleaned while achieving no corrective result. I have even replaced the ECM twice.

I have even had it to the dealer to have the code "serviced" and they contacted Toyota Tech and they said, "It cant throw that code, the 1993 does not have the sensor".

If it doesn't have the sensor, there is no plug for me to "jumper out.".

I have read that I need to "trick" the input at the ECM into thinking there is a sensor that is working properly.

Do I have another option to resolve this?

Thanks for the input of the brain trust here.
 

LandLocked93

SILVER Star
Joined
Jun 11, 2018
Messages
637
Location
Colorado
What is the actual born-on date of your truck?

Is your CEL on, or does it appear after a few minutes of operation?
Does it run like poop?
Are you facing an emissions test?
If no on all those, you could...stop checking for codes?

I've found paying mind to ECM codes, especially on OBD1 trucks, can lead you down a dark way. Not to say they have no purpose, but I've found them to be more like suggestive guidelines than absolute rules. OBD2 is far more nagging and guilt-trippy.
Only if my CEL appears during normal operation - and even then only if it stays on, which has never happened - do I bother to check for codes.

edit: and just for reference, I've removed the PAIR valves and disabled the EGR using the loopback method and still no codes recorded and no CEL.
 
Last edited:
Joined
Feb 7, 2009
Messages
2,544
If I remember right you might not have the sensor, but the wiring is there, it should have a factory plug plugged into it with a jumper on the engine harness there if I am correct you might be missing that plug off with the jumper. Would simply need to insert a jumper wire into the harness.
 

Traakon

SILVER Star
Joined
Mar 22, 2015
Messages
258
Location
Queen Creek, Az.
What is the actual born-on date of your truck?

Is your CEL on, or does it appear after a few minutes of operation?
Does it run like poop?
Are you facing an emissions test?
If no on all those, you could...stop checking for codes?

I've found paying mind to ECM codes, especially on OBD1 trucks, can lead you down a dark way. Not to say they have no purpose, but I've found them to be more like suggestive guidelines than absolute rules. OBD2 is far more nagging and guilt-trippy.
Only if my CEL appears during normal operation - and even then only if it stays on, which has never happened - do I bother to check for codes.
What is the actual born-on date of your truck?

Is your CEL on, or does it appear after a few minutes of operation?
Does it run like poop?
Are you facing an emissions test?
If no on all those, you could...stop checking for codes?

I've found paying mind to ECM codes, especially on OBD1 trucks, can lead you down a dark way. Not to say they have no purpose, but I've found them to be more like suggestive guidelines than absolute rules. OBD2 is far more nagging and guilt-trippy.
Only if my CEL appears during normal operation - and even then only if it stays on, which has never happened - do I bother to check for codes.

edit: and just for reference, I've removed the PAIR valves and disabled the EGR using the loopback method and still no codes recorded and no CEL.

edit: and just for reference, I've removed the PAIR valves and disabled the EGR using the loopback method and still no codes recorded and no CEL


We have had a constant CEL for the EGR since we purchased the 'Cruiser. Its BOD is 05/93.

When we first brought her home to us I spent a lot of time, money, and energy trying to get it resolved and eventually took it to CBT for the issue. That is when the Toyota Factory Tech offered his input that "It can't throw that code, it doesn't have the sensor."

It ran OK, and since it was my wife daily and she works from home, it really did not see many miles/month. She just learned to ignore the CEL.

I have finally decided to dig into the issue again with a brave new outlook.

The 'Yota Tech suggested inserting a 4.7k resistor in the ECU harness between the EGR sensor input and ground. That is something I have been putting off hoping I could find another solution.
 

Traakon

SILVER Star
Joined
Mar 22, 2015
Messages
258
Location
Queen Creek, Az.
If I remember right you might not have the sensor, but the wiring is there, it should have a factory plug plugged into it with a jumper on the engine harness there if I am correct you might be missing that plug off with the jumper. Would simply need to insert a jumper wire into the harness.
Thanks for that. I have been all over the harness in the area where it "might" be and found nothing. CBT found nothing as well.
 

LandLocked93

SILVER Star
Joined
Jun 11, 2018
Messages
637
Location
Colorado
Have you checked out this thread? It shows the loop back for EGR disable and also the temp sensor plug jumper.
 

Traakon

SILVER Star
Joined
Mar 22, 2015
Messages
258
Location
Queen Creek, Az.
Have you checked out this thread? It shows the loop back for EGR disable and also the temp sensor plug jumper.

Thanks, I have read every page of every thread relating to this.

The "Redneck" solution would be great IF I had the relevant connector to put the jumper in.
 

LandLocked93

SILVER Star
Joined
Jun 11, 2018
Messages
637
Location
Colorado
Thanks, I have read every page of every thread relating to this.

The "Redneck" solution would be great IF I had the relevant connector to put the jumper in.
The wires for the connector should be in the big harness. Perhaps a PO removed the actual connector and joined the wires to each other via a resistor. Then wrapped the wires back up in the harness. And that connection has perished.
 
Joined
Feb 7, 2009
Messages
2,544
It is there unless someone cut it out, buddy has the same setup. No temp sensor, wire harness for the engine with factory plug in it. I just don’t remember if it comes out behind the head or by the injectors
 
Joined
Mar 17, 2019
Messages
169
Location
Georgia
It is there unless someone cut it out, buddy has the same setup. No temp sensor, wire harness for the engine with factory plug in it. I just don’t remember if it comes out behind the head or by the injectors
@ajax1 is correct, it's there unless someone has already modified it. It should be by the EGR, about where the temp sensor would be if it had one. As you can see below, close enough to fall on the EGR pipe itself when the tape / clips fail. My 80 was built a month after yours and this is a pic of my harness....

IMG_20200829_162050.jpg


You can see from my neat cutaway plug there, it's just a really nice jumper, probably with a resistor potted in. If yours is gone, the "redneck" resistor is the way to go. Functionally it is the same thing as Toyota did factory. The factory plugs were unobtanium when I looked for one, they were the popular trick to delete the EGR and get rid of the code / light before I got in to the 80 game it seems. NLA from Toyota.

Good luck !

Jason
 

Traakon

SILVER Star
Joined
Mar 22, 2015
Messages
258
Location
Queen Creek, Az.
To follow up on this. I split the harness along the firewall open and found no connector either loose or tucked away. I didn't find anything that resembled one that might have been cut out. I have no idea what was done to this 80 but I know what I did.

Following the directions given me by the Toyota Tech when she was at CBT, I pulled the ECM and the connectors and inserted a 4.7k resistor between the ECM input for the EGR and ground. Reset the codes and so far, no more CEL.
 
Joined
Mar 17, 2019
Messages
169
Location
Georgia
To follow up on this. I split the harness along the firewall open and found no connector either loose or tucked away. I didn't find anything that resembled one that might have been cut out. I have no idea what was done to this 80 but I know what I did.

Following the directions given me by the Toyota Tech when she was at CBT, I pulled the ECM and the connectors and inserted a 4.7k resistor between the ECM input for the EGR and ground. Reset the codes and so far, no more CEL.

Glad you got rid of the code. Since I'm working on this thing right now anyway, here you go. Maybe this will help someone later. In this pic you are looking through the EGR valve (it's off and the hole is covered with this really neat keychain thing I found online to keep the mice out until I replace it...). The connector is in the shadows in the middle of the triangle made by the engine wiring harness (foil tape wrapped), the rear EGR valve stud, and the heater hose, just above the fuel rail banjo bolt. I think it comes off the engine harness with the #5 or #6 injector plug.

PXL_20210424_203455136.jpg



Jason
 

Users who are viewing this thread

Top Bottom