EPC harness review. (seems just the trans harness 57 matters.) there are no pages , that shows, 3AT/4AT wiring differences.
all things equal (doorcount,2wd/4wd/AT/year/8v/16v)
the harness id's and factors below. (only usa, outside usa vast count)
I.D: , what..harness
1: main, there are 30 main harnesses, but AT3 and AT4 are same, all else same! (doors/engine/2wd/4wd/years/etc)
31: cluster IP, harness years/and doors. (x5)
35:floor, all same but door count.
39:rear lamp , just door count.
43- engine, year, doors , 8v and 16v , m/t and AT (means both)2wd/4wd there are 11 harnesses here.
45-INJectors, just 1 for 16v.
57-tranmission harness (9 total types) varies by door /at/mt/2wd/4wd. but all AT the same , all else the same. and one calif verion(?) wow.
there are other wiring assemblies (117 line items)
but above are key , to topic.
seem if car is same doors, 4wd , the AT trans harness for 3speed works for 4speed.
and same with ECU if all is same. but trans type.
This is because(my best guess) the AT- version ECU sends the same load data serial data to the TCM even if the TCM is missing.(on 3AT)
the data is just sent blindly, until later years. much later.
On newer cars if the ECU cant send commands to the TCM it sets up errors.
P1600 is one such error, 1996+ (and you fail smog tests ,just for that one code)
so the old ECU send data blindly, (a good thing in this case)
try to understand the 4sp has no 3AT vacuum modulator (vacuum is load on all 3speeds)
the 4speed uses load data from the ECU, and will never shift correctly lacking that serial load data from ECU to TCM.
what that means is up hills it may not down shift. see? it still auto-shifts , but cant do it correctly. lacking correct ECU.
how is that?
all things equal (doorcount,2wd/4wd/AT/year/8v/16v)
the harness id's and factors below. (only usa, outside usa vast count)
I.D: , what..harness
1: main, there are 30 main harnesses, but AT3 and AT4 are same, all else same! (doors/engine/2wd/4wd/years/etc)
31: cluster IP, harness years/and doors. (x5)
35:floor, all same but door count.
39:rear lamp , just door count.
43- engine, year, doors , 8v and 16v , m/t and AT (means both)2wd/4wd there are 11 harnesses here.
45-INJectors, just 1 for 16v.
57-tranmission harness (9 total types) varies by door /at/mt/2wd/4wd. but all AT the same , all else the same. and one calif verion(?) wow.
there are other wiring assemblies (117 line items)
but above are key , to topic.
seem if car is same doors, 4wd , the AT trans harness for 3speed works for 4speed.
and same with ECU if all is same. but trans type.
This is because(my best guess) the AT- version ECU sends the same load data serial data to the TCM even if the TCM is missing.(on 3AT)
the data is just sent blindly, until later years. much later.
On newer cars if the ECU cant send commands to the TCM it sets up errors.
P1600 is one such error, 1996+ (and you fail smog tests ,just for that one code)
so the old ECU send data blindly, (a good thing in this case)
try to understand the 4sp has no 3AT vacuum modulator (vacuum is load on all 3speeds)
the 4speed uses load data from the ECU, and will never shift correctly lacking that serial load data from ECU to TCM.
what that means is up hills it may not down shift. see? it still auto-shifts , but cant do it correctly. lacking correct ECU.
how is that?
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