Reading OBD1 codes

ROBERTW972

MEMBER
1994 LEXUS GS 300
3.0L
6 CYL
2WD
AUTOMATIC
260,000 MILES

I am trying to get the codes off of my car. I connected the wire from E1 to TE1, and turned the car to ignition. The check engine light flashes and gives me a code of 7 and 1 (71) which is EGR system fault, but also the overdrive light is flashing a series of flashes, what looks to be a 4 and a 2. My question is, is that a separate set of codes, is that also a code, or something else altogether?

Your input is appreciated.

Robert W.

1 Reply

STEVE W.

MECHANIC
13,576 POSTS

Individual codes. But likely related, with the second code causing the first one.
Code 71 in the engine control module for the EGR System Malfunction
These are the setting criteria for that code
Exhaust Gas Re-circulation gas temperature is 70°C (158°F) or below for one to four minutes under the following conditions; (2 trip detection logic) Engine coolant temperature is 63°C (145°F) or more. Exhaust Gas Re-circulation operation possible (A/T in 3rd speed, A/C ON, 60 mph, Flat road).

Notice the speed and gear inputs needed for the EGR to operate? The below code deals with the ECMs speed input for it's calculations. If it is not reading correctly it could cause the EGR to either not operate or operate in the wrong time periods.

Code 42 is in the transmission control module for number one speed sensor output failure on the transmission. To test it you really need a scope to watch the signal output at around thirty five mph. I would check the connection for corrosion and if it is okay and the speedometer is working it could be a fault in the buffer in the instrument panel or a fault in the ECM.

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Reading OBD1 codes

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