INTRODUCTION
Pin voltage charts are supplied to reduce diagnostic time. Checking pin voltages at the Electronic Control Unit (ECU) determines whether it's receiving and transmitting proper voltage signals. Charts may also help determine if ECU harness is shorted or opened.
Note. ECU pin voltages for LS400 apply to 1991 models only.
Note. All voltage tests should be performed with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in testing procedures. Voltage readings may vary slightly due to battery condition or charging rate.
Scheme 1
ES250
| ECU Terminals | Conditions | Voltage |
|---|---|---|
| BATT & E1 | " | 10-14 |
| IG SW & E1 | Ignition On | 10-14 |
| M-REL & E1 | Ignition On | 10-14 |
| B & E1 | Ignition On | 10-14 |
| B1 & E1 | Ignition On | 10-14 |
| IDL & E2 | Ignition On, Throttle Valve Open | 4-6 |
| VTA & E2 | Ignition On, Throttle Fully Closed | .1-1 |
| " | Ignition On, Throttle Valve Open | 3.2-4.2 |
| VC & E2 | Ignition On, Throttle Fully Closed | 3.7-4.3 |
| " | Ignition On, Throttle Valve Open | .2-.5 |
| VS & E2 | Engine Idling | 1.6-4.1 |
| " | 3000 RPM | 1-2 |
| No. 10 & EO1 | Ignition On | 10-14 |
| No. 10 & EO2 | Ignition On | 10-14 |
| No. 20 & EO1 | Ignition On | 10-14 |
| No. 20 & EO2 | Ignition On | 10-14 |
| No. 30 & EO1 | Ignition On | 10-14 |
| No. 30 & EO2 | Ignition On | 10-14 |
| THA & E2 | Ignition On, Intake Air Temp 68°F (20°C) | 1-3 |
| THW & E2 | Ignition On, Coolant Temp. 176°F (80°C) | .1-1 |
| STA & E1 | Engine Cranking | 6-14 |
| IGT & E1 | Cranking Or Idling | .7-1 |
| ISC1 & E1 | Ignition On | 9-14 |
| ISC2 & E1 | Ignition On | 9-14 |
| ISC3 & E1 | Ignition On | 9-14 |
| ISC4 & E1 | Ignition On | 9-14 |
| W & E1 | CHECK Engine Light Off, Engine Idling | 10-14 |
| A/C & E1 (1) | Ignition On, A/C On | 8-14 |
| ACT & E1 (1) | Ignition On, Blower Switch On | 4-6 |
| T1 & E1 | Ign. On, TE1 & E1 Not Connected | 4-6 |
| T2 & E1 | Ignition On, TE1 & E1 Connected | 0-.5 |
| NSW-E1 (2) | Ignition On, Gear Shift In P Or N | 0-2 |
| BK & E1 (2) | Brake Pedal Depressed | 10-14 |
| (1) With air conditioning. (2) With Electronic Controlled Transmission (ECT). | ||
| (1) | With air conditioning. |
| (2) | With Electronic Controlled Transmission (ECT). |
ECU VOLTAGE SPECIFICATIONS
Scheme 2
| ECU Terminals | Conditions | Voltage |
|---|---|---|
| BATT & E1 | " | 10-14 |
| IG SW & E1 | Ignition On | 10-14 |
| B (B1) & E1 | Ignition On | 10-14 |
| IDL & E2 | Ignition On, Throttle Valve Open | 4-6 |
| VC & E2 | Ignition On | 4-6 |
| VTA & E2 | Ignition On, Throttle Fully Closed | .1-1 |
| " | Ignition On, Throttle Valve Open | 3-5 |
| KS & Body Gnd. | Ignition On | 4-6 |
| " | Cranking or Running | 2-4 |
| VC & Body Gnd. | Ignition On | 4-6 |
| THA & E2 | Ignition On, Intake Air Temp 68°F (20°C) | 1-3 |
| THW & E2 | Ignition On, Coolant Temp 176°F (80°C) | .1-1 |
| No. 10 & EO1 | Ignition On | 10-14 |
| No. 10 & EO2 | Ignition On | 10-14 |
| No. 40 & EO1 | Ignition On | 10-14 |
| No. 40 & EO2 | Ignition On | 10-14 |
| STA & E1 | Cranking | 6-14 |
| ISC1 & E1 | Ignition On | 9-14 |
| ISC4 & E1 | Ignition On | 9-14 |
| IGT & E1 | Engine Idling | .7-1 |
| W & E1 | CHECK ENGINE Light Off, Engine Running | 8-14 |
| AC & E1 | A/C On | 0-2 |
| TE1 & E1 | Ignition On, Check Connector TE1 & E1 Not Connected | 4-6 |
| " | Ignition On, Check Connector TE1 & E1 Connected | 0-1 |
| NSW & E1 | Ignition On, Gear Shift In P Or N | 0-1 |
| " | Ignition On, Gear Shift Not In P Or N | 10-14 |
ECU VOLTAGE SPECIFICATIONS (LS400)