CHECK GAUGES Indicator Lamp
The CHECK GAUGES indicator lamp comes on under the following conditions:
| • | Engine oil pressure is at or below approximately 34 kPa (5 psi). |
| • | Engine coolant temperature is at or over approximately 118°C (245°F), as received from the multifunction alarm module. |
The ignition switch must be in the RUN position in order to power the CHECK GAUGES lamp driver. The IGN 1 circuit breaker in the IP fuse block provides power to this lamp. The multifunction alarm module grounds the lamp driver.
The CHECK GAUGES lamp remains lit after the engine starts until the engine oil pressure exceeds the low oil pressure setpoint.
LOW COOLANT Indicator Lamp (Hydraulic Brakes Only)
The LOW COOLANT indicator lamp comes on when the coolant level in the radiator becomes low. When the ignition switch is in the RUN position, the IGN 1 circuit breaker provides the battery voltage from the multifunction alarm module.
The multifunction alarm module performs the following functions:
| • | Monitors resistance to ground from the low engine coolant level indicator switch. |
| • | Provides a ground to the LOW COOLANT indicator lamp when sensor resistance indicates a low coolant level. |
This sensor has a resistance of 50,000 ohms or more when the coolant level is low. The sensor resistance decreases to about 10,000 ohms when the radiator is full.
The LOW COOLANT indicator lamp comes on when the resistance to ground is greater than 50,000 ohms.
Oil Pressure Gauge
When the ignition switch is in the RUN position, battery voltage from the IGN 1 circuit breaker in the IP fuse block powers the oil pressure gauge.
If the current through the oil pressure gauge and the oil pressure sensing element is high, the gauge moves toward the 0 kPa (0 psi) indication. If the current through the gauge and sensor decreases, the gauge moves toward the 550 kPa (80 psi) indication.
Two magnetic coils pass the current through the oil pressure gauge. The vertical coil connects directly to ground. The horizontal coil ground is through the oil pressure sensing element. Some of the current always passes through the vertical coil. The percentage of total current that goes through the horizontal coil depends on the resistance of the oil pressure sensing element.
The oil pressure sensing element produces a resistance of approximately 0 ohms when the oil pressure is zero, and 88 ohms at 550 kPa (80 psi). With a lower resistance, a greater percentage of total current passes through the horizontal coil and the gauge moves to 0 kPa (0 psi). When the oil pressure is high, a smaller percentage of current flows through the oil pressure gauge horizontal coil, and the gauge moves toward 550 kPa (80 psi).
When the multifunction alarm module senses a high temperature or a low oil pressure condition, the module grounds the CHECK GAUGES cluster telltale input terminal A2 (LP4/L21) or B7 (LG5). The oil pressure setpoint is at approximately 34 kPa (5 psi).
The oil pressure gauge accuracy is adequate for normal operator usage because the gauge provides a reasonably accurate indication of engine oil pressure from which sudden or long term changes may be identified. The sensing element response is essentially linear over the operating range. The following are the gauge accuracy specifications:
| • | 3.5 degrees (angular) at 0 kPa (0 psi) |
| • | 7 degrees at 550 kPa (80 psi) |
Changes in battery voltage do not affect the gauge accuracy.
Speedometer/Odometer
The speedometer and odometer operate through solid state circuitry inside the instrument cluster. The IP fuse block IGN 1 circuit breaker through CKT 39 (PNK) powers the instrument cluster. The speedometer receives a square wave 4000 PPM (pulses per mile) signal from the vehicle speed sensor buffer through CKT 389 (DK GRN). The solid state electronics positions the speedometer pointer in response to the pulse rate. The electronics also drive the odometer indication in response to the pulse rate over time.
The speedometer rated accuracy at 104 km/h (65 mph) is plus or minus 3 km/h (2 mph) or 101-107 km/h (63-67 mph). At 32 km/h (20 mph), the rated accuracy is plus or minus 6 km/h (4 mph) or 26-38 km/h (16-24 mph). Variations in voltage and inaccuracies in the other circuit components may increase the error.
Tachometer
A signal received from the generator drives the tachometer for the diesel engine. A logic module in the IP cluster interprets the signal from the generator, and positions the tachometer pointer in response to the pulse rate.
The ignition coil provides the tachometer signal for the gasoline engine. A logic module in the IP cluster interprets the signal from the distributor, and positions the tachometer pointer in response to the pulse rate.
Temperature Gauge
Magnetic fields of two coils move the pointer of the temperature gauge, a 37°C (100°F) and a 125°C (260°F) coil. The two coils are oriented at right angles so that the magnetic fields interfere with each other.
When the ignition switch is in the RUN position, battery voltage is available from the IGN 1 circuit breaker through CKT 39 (PNK) to the instrument cluster.
Current flows through the 37°C (100°F) coil which places the pointer at 37°C (100°F) (low temperature) if there is little current through the 125°C (260°F) coil. If the current through the 125°C (260°F) coil is high, then the pointer moves toward the 125°C (260°F) (high temperature) indication.
The current that passes through the 125°C (260°F) coil has the following two paths to ground:
- Some current passes through the fixed resistance of the 37°C (100°F) coil and to ground G101 through CKT 150 (BLK).
- The rest of the current will go to ground through the variable resistance of the temperature sensor.
The engine coolant temperature sensor produces a resistance of approximately 1305 ohms when the temperature is 40°C (100°F). Because of this high resistance, more current flows through the 37°C (100°F) coil and the pointer moves toward 100.
The sensor resistance is approximately 61.9 ohms at 118°C (245°F). With this low resistance, more current passes through the temperature sensor, and not the 37°C (100°F) coil. The pointer moves toward 125°C (260°F).
When the multifunction alarm module senses a high temperature or a low oil pressure condition, the module grounds the CHECK GAUGES indicator lamp input terminal B. The temperature setpoint is at approximately 61.9 ohms or 118°C (245°F).
The temperature gauge accuracy is adequate for normal operator usage because the gauge provides a reasonably accurate indication of engine coolant temperature from which sudden or long term changes may be identified. The sensing element response is non-linear over the operating range and this limits accuracy. The following are the gauge accuracy specifications:
| • | 3.5 degrees (angular) at 125°C (260°F) |
| • | 7 degrees at 37°C (100°F) |
Changes in battery voltage do not affect the gauge accuracy.
Voltmeter
The voltmeter indicates battery voltage when the ignition switch is in the RUN position. The voltmeter measures generator voltage when the engine is running. The normal generator voltage is 14 volts.
The battery voltage, without the engine running, depends on ambient temperature, and may be as low as 9.6 volts.
The IGN 1 circuit breaker through CKT 39 (PNK) supplies voltage to the voltmeter. Grounding for the single coil indicator is through CKT 150 and CKT 250 (BLK) to G102 (LP4/L21) or G101 (LG5).
