I am a newbie to this forum so please be gentle. My 86 FZJ80 LC threw the dreaded P0402 code – excess EGR flow. Went through the forum to glean wisdom and checked all the obvious suspects: VSV, EGR modulator, EGR valve all check out. All new hoses and vacuums present where they are supposed to be. EGR Temperature sensor has correct impedance at room temperature (have not checked at elevated temperature yet). No observable leaks at cat gasket but unsure how to test that thoroughly?
My understanding from the forum is that the VSV controls the release of vacuum generated by the modulator to regulate the opening of the EGR valve. When activated the VSV is closed, vacuum is retained, and the VSV opens the EGR valve to recirculate exhaust gases. When open (not-activated) vacuum is vented closing the EGR valve. The ECM controls VSV activation based upon inputs from the EGR temperature sensor and TPS. There are two wires to the VSV – white/blue and red/yellow which (I believe) come directly from the ECU. According to an earlier post there is power going to the VSV valve through the yellow/red wire at all times and activation is though a ground signal from the ECM though the Blue/white wire.
My P0402 means that the EGR is being opened at inappropriate times (idle when cold or at full throttle). I find that at idle, when cold, I have 12V across the VSV terminal indicating activation promoting EGR flow, which is not what I expected under those conditions making me suspect a problem with the wiring harness. I tested the voltage and impedance at the VSV connector located by the TPS with the ignition on and with the engine off and also running and got the following values: Yellow/Red – 12.2 – 14.6 V(engine running) Blue/white – ground to earth. I then unplugged the harness from the ECU and found that both Yellow/Red AND Blue/white were grounded?
This implies I have an open ground to earth to the VSV on the blue/white wire at all times, which I would not expect if the ECU controls activation by periodic grounding. A permanently closed VSV would explain my P0402 code.
Unfortunately I don’t have and FSM or a wiring diagram for the engine harness. Could someone quickly unplug their VSV lead at the connector by the throttle body and see if the Blue/white is meant to be grounded with ignition off and on when at idle cold. Also does anyone know why I would have white/yellow grounded when the ECU is disconnected? I am very confused. Any help would be much appreciated.
My understanding from the forum is that the VSV controls the release of vacuum generated by the modulator to regulate the opening of the EGR valve. When activated the VSV is closed, vacuum is retained, and the VSV opens the EGR valve to recirculate exhaust gases. When open (not-activated) vacuum is vented closing the EGR valve. The ECM controls VSV activation based upon inputs from the EGR temperature sensor and TPS. There are two wires to the VSV – white/blue and red/yellow which (I believe) come directly from the ECU. According to an earlier post there is power going to the VSV valve through the yellow/red wire at all times and activation is though a ground signal from the ECM though the Blue/white wire.
My P0402 means that the EGR is being opened at inappropriate times (idle when cold or at full throttle). I find that at idle, when cold, I have 12V across the VSV terminal indicating activation promoting EGR flow, which is not what I expected under those conditions making me suspect a problem with the wiring harness. I tested the voltage and impedance at the VSV connector located by the TPS with the ignition on and with the engine off and also running and got the following values: Yellow/Red – 12.2 – 14.6 V(engine running) Blue/white – ground to earth. I then unplugged the harness from the ECU and found that both Yellow/Red AND Blue/white were grounded?
This implies I have an open ground to earth to the VSV on the blue/white wire at all times, which I would not expect if the ECU controls activation by periodic grounding. A permanently closed VSV would explain my P0402 code.
Unfortunately I don’t have and FSM or a wiring diagram for the engine harness. Could someone quickly unplug their VSV lead at the connector by the throttle body and see if the Blue/white is meant to be grounded with ignition off and on when at idle cold. Also does anyone know why I would have white/yellow grounded when the ECU is disconnected? I am very confused. Any help would be much appreciated.
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