The EST circuit has been on G.M. vehicles for quite a few years. So, EST can be seen on a vehicle with a high-energy ignition distributor (HEI) or, vehicles that are equipped with a direct ignition system. (DIS) {Distributor �less}
Why EST?To provide improved engine performance, better fuel economy, and to better control exhaust emissions, the computer controls spark advance (timing) with the EST system. To calculate spark advance the computer uses information from the manifold absolute pressure (MAP) sensor and the coolant temperature sensor (CTS) as well as engine RPM.How spark advance is calculated:� Low MAP (low engine load) = more spark advance
� Cold engine = more spark advance
� High MAP (high engine load) = less spark advance
� Warm engine = less spark advance
� High RPM = more spark advance
� Low RPM = less spark advanceThe system.The EST system consists of the ignition module, computer (ECM/PCM), and the connecting wiring. There are four circuits to this system.The circuits and their functions:� Reference.
This circuit provides the computer with RPM information. If this circuit becomes open or shorted to ground the engine will not run, because the computer will not operate �trigger� the fuel injectors.
A common saying here is, no reference no run.
� Reference ground.
This circuit is grounded in the ignition module and the computer; it makes sure the ground circuit has no voltage drop, which could affect vehicle performance. I have found an open in this circuit can cause a vehicle �no start� as well as a false code 42/E23.
� By-pass.
The computer applies 5 volts to this circuit to switch timing control from the ignition module to the computer. The computer is telling the ignition module that it will control the timing. An open or a short to ground of this circuit will set the code and the engine will run on base timing. (Plus a small amount of advance built into the ignition module.)
� EST.
This circuit triggers the ignition module. The computer does not know what the actual timing is, what it does know is when it gets a reference signal. It uses this reference signal as a base point and advances or retards the spark from that point. So, if on vehicles where the base timing is adjustable, and the base timing is set incorrectly, the spark curve will be off through its entire range by the amount that the base timing is misadjusted. An open or short to ground in this circuit will set the code and cause the engine to run on ignition module timing.Why the computer flags this code.What we have here is a failure to communicate.� The ignition module and the computer are in constant communication when the engine is in operation. (Over 400 RPM.)With the computer telling the module the correct timing. If communication is lost or a circuit becomes infected with false signals (bad grounds, short to battery +, Electro Magnetic Interference {spark plug wires to close to circuit wiring}, oil contamination of the circuit connectors and wiring) then the computer will turn timing control back to the ignition module and flag the code.Possible causes:� EST circuit open or grounded.
� Bypass circuit open or grounded.
� Reference Ground circuit open or shorted to battery� +.
� A bad computer to engine circuit ground.
� A defective ignition module.
� A defective computer. If you are testing a vehicle for this code check the routing of the spark plug wires making sure they are not to close to the EST circuit(s) wiring. Check the connector terminals making sure they are not over-sized or oil contaminated. Check the entire wiring of the circuits for chaffing,
short(s) ground.
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i have a 2000 mazda 626 with a 1744 code. i was able to pull the code but my scanner wont tell me what it is for. what does this code represent and how do i fix it?
You have to fix the cause of the code that turned the light on. You will need a scanner to read the code.
Electronic Spark Timing (EST) bypass circuit or EST circuit is grounded or open. HEI Module may be the cause
The light could come on for a number of reasons. The vehivle would have to be hooked up to a scanner to determine the engine code or codes. After you determine the codes you can isolate and fix the probelem. If the check engine light is on there will be a computer code that will appear on the scanner.
checking and found burned fuse, replaced burns quick, checked scanner diagnosis and need to pin check oxygen sensors, this burns fuses without sensors plugged in, we are suspecting shoprted wire or ecm.
replace the ignition module Its under the rotor inside the distributer cap
You need to use an OBDII scanner (available at your local auto parts store) to see what the diagnostic code is. Depending on what what fault code is, you either have to fix something or you can clear it and see if the code returns. You can clear the code (turn out the light) with the OBDII Scanner. Personally i bought a ScanGaugeII for this and it's AWESOME! the Haynes and Chilton repair manuals will help you figure out what the code means.
You need to obtain a troubleshooting chart for that code. If I recall, it has to do with the Evaporative system.
if code 44 is a lean code and 45 is a rich code if both are present suspect faulty o2 sensor if just code 44 check fuel pressure it should never drop below 10psi. then block off the return line from the throttle body. pressure should raise to +18psi. if not replace fuel pump.
Find where the compressor assembly is on your vehicle. Unplug the connector with all wires. Set your DVOM to ohms and check the resistance on the compressor side of the connector of the light blue wire and the gray wire..... it should be 18-45ohms. That is the exhaust valve solenoid which the computer throws code CO660 when it's bad. There's no repair for it, just replace the whole compressor assembly. if you diagnose the GM by GM MDI, you can repair it or reset by some obd2 code scanner from vipprogrammer.com
PCM code P0700 = Transmission Control System Malfunction That just means that the transmission computer has also set a code. You need to also check the TCM with a scanner to know what code it set to know possible causes.
find out what it is.... (preferably with a scanner) fix it... , clear codes with scanner