CEL Question (1 Viewer)

Joined
Nov 20, 2020
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17
Location
San Antonio, TX
Hi Folks, just a qq: my CEL has been lit for a few weeks now (code 71 EGR). I have not yet fixed the egr but if I reset the cel by unhooking battery cable, the light will turn off but inevitably come back on after a few miles (as expected).

however, today I noticed the cel was off when I started the truck but I did not remove battery cable prior. My question is: will the cel automatically turn off if the issue is not detected? My understanding was that once the computer trips the CEL, it will stay on until the ecu is reset (power/fuse pulled), even if the underlying issue (egr) is fixed. Hence, trying to understand why the light would now be off.

thanks!
 

D0g

Joined
Mar 31, 2016
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Los Angeles
If you have a scan tool check if you have any stored codes and check the readiness monitors as well.
 
Joined
Nov 20, 2020
Messages
17
Location
San Antonio, TX
If you have a scan tool check if you have any stored codes and check the readiness monitors as well.
I guess as a first step I can see if the paperclip will result in any flashes. If not, can go to a shop with a scanner.

are readiness monitors a thing with the obd1 trucks? Forgive my ignorance
 

D0g

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Messages
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Location
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I guess as a first step I can see if the paperclip will result in any flashes. If not, can go to a shop with a scanner.

are readiness monitors a thing with the obd1 trucks? Forgive my ignorance
No i assume you have a pre 96 truck try the paper clip it will read stored codes
 

richardlillard1

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Mar 15, 2014
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On early 93 and 91-92 models, the CA emissions specs for the EGR have a temp sensor. On non-CA emission 80s, there is a jumper on the wiring harness. Unplug the temp sensor, put in a paperclip, drive until the light goes off.
 

SmokingRocks

I bought a Cruiser to keep miles off my Cruiser
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Oct 6, 2014
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Colorado
Yes the cel will turn off on its own under certain circumstances.

for example if the problem is detected then the cel will light. (See your fsm for details on the items that will illuminate a CEL). Basically if the issue happens the light comes on, but is the issue isn’t seen by the ecu in a a set number of cycles (where it should’ve seen the issue again) the light will go off.
 

richardlillard1

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FSM procedure for testing the repair (paperclip):
E7BF4C13-91C5-4118-81C7-9054C664D766.jpeg


Performing this test after installing the jumper should reset and test the system to confirm it solved the issue. This is the equivalent of the 4.7k ohm resistor for OBD II trucks.
 
Joined
Nov 20, 2020
Messages
17
Location
San Antonio, TX
FSM procedure for testing the repair (paperclip):
View attachment 2547129

Performing this test after installing the jumper should reset and test the system to confirm it solved the issue. This is the equivalent of the 4.7k ohm resistor for OBD II trucks.

perfect thanks! This has me seriously considering just deleting egr altogether or at least removing and capping some vacuum lines...
 

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