Instrument Panel (except Syclone) GMC Sonoma Syclone

STANDARD INSTRUMENT PANELS

Standard mechanical instrument panels on all models are designed to permit the removal and installation of all control switches, gauges and illuminating bulbs from the driver's side. The standard instrument panels are equipped with warning lights only. Optional equipment instrument clusters come equipped with gauges and digital speedometer, as well as standard and optional warning lights.

ELECTRONIC INSTRUMENT CLUSTER

This instrument cluster is a solid-state device that uses a digital display for speedometer/odometer information and bar graph displays for gauge information. This electronic device receives input signals from the following components and systems

1. English/Metric switch
2. Odometer trip/reset switch
3. Battery, charging, ignition and lighting systems
4. Oil, fuel and temperature sending units
5. Digital Ratio Adapter Controller (DRAC)
6. Vehicle speed sensor

Vehicle speed sensor (VSS) signal originates at transmission tone wheel on tailshaft. This AC voltage signal is changed to a digital signal for speedometer use by Digital Ratio Adapter Controller (DRAC). The electronic instrument cluster does not contain any serviceable components and is serviced as a complete assembly.

BRAKE WARNING LIGHT SYSTEM OPERATION

Warning system consists of a Red BRAKE warning light on instrument cluster/panel, a BRAKE warning light/pressure differential switch (located on brake combination/proportioning valve) and a parking brake engagement telltale switch. If brake hydraulic system malfunctions, or if parking brake is NOT fully released, BRAKE warning light will illuminate.

ABS (OR ANTI-LOCK) WARNING LIGHT SYSTEM

An Amber ABS or ANTI-LOCK warning light will illuminate when ignition is turned on, and if no problem exists, light will go out when engine starts. If amber ABS warning light stays on at any time, conventional brake system will still be operational, but without anti-lock assistance. If both BRAKE and ABS warning lights illuminate at same time while driving, stop vehicle carefully and park vehicle until systems can be repaired.

Standard Panel

Warning system consists of a battery symbol warning light on instrument cluster/panel. One side of warning light bulb is connected to alternator field circuit and other side of bulb is connected to ignition power circuit. If charging system malfunction is detected, warning light will illuminate.

Electronic Digital Instrument Cluster

If charging system malfunctions, signal box around voltmeter gauge battery symbol will illuminate and flash at full intensity.

"S" & "T" Series (Gauge Cluster)

This optional equipment warning light illuminates when engine coolant temperature is too high or when engine oil pressure is too low. Warning signals from engine coolant temperature and/or oil pressure switches are monitored by CHECK GAGES light driver. Light driver is an integral part of coolant temperature gauge circuit board.

Warning light switches are separate units from gauge sending units. Coolant temperature warning system uses engine mounted temperature switch. When coolant overheats, switch closes and CHECK GAGES warning light illuminates. Coolant switch closing temperature is 257°F (125°C).

Oil pressure warning system uses an oil pressure switch. When oil pressure drops below 4 psi (.28 kg/cm 2 ), switch closes and illuminates CHECK GAGES warning light on instrument cluster. Oil pressure warning switch is mounted next to oil pressure sending unit on vehicles equipped with gauges. Warning switch is mounted in place of sending unit on vehicles not equipped with gauges.

COOLANT TEMPERATURE GAUGE

Coolant temperature gauge measures electrical current resistance from coolant temperature sending unit mounted in cylinder head. Sending unit has a resistance of 55 ohms at 260°F (127°C) and 1400 ohms at 100°F (38°C). As coolant temperature increases, current flow through sending unit to gauge increases due to less resistance, causing gauge pointer to move toward HOT.

Standard Panel (Without Gauges)

Warning system consists of temperature switch and instrument cluster warning light. When coolant overheats, switch closes and warning light illuminates. Switch closing temperature is 257°F (125°C).

Standard Panel (With Gauges)

See CHECK GAUGES LIGHT DESCRIPTION .

If coolant temperature reaches 245°F (118°C), engine mounted coolant temperature switch signals box around temperature gauge thermometer symbol to illuminate and flash at full intensity.

DIGITAL RATIO ADAPTER CONTROLLER

Digital Ratio Adapter Controller (DRAC) is a solid-state device used to change AC voltage signal from the VSS to a digital signal for speedometer operation.

DRAC is matched to the final drive ratio of each vehicle. If the final drive ratio is changed for any reason (i.e. tires or gears), DRAC must be replaced to maintain accurate speedometer/odometer reading.

Note. Incorrect DRAC calibration may adversely affect Rear Wheel Anti-Lock Brakes (RWAL), Electronic Control Module (ECM), and Cruise Control Module (CCM).

FUEL GAUGE

Fuel gauge is an electrical instrument that measures current flow from variable-resistance fuel gauge sending unit in fuel tank. When fuel level in tank is high, fuel gauge sending unit resistance is high. Fuel sending unit is located on or near top of fuel tank. Some units use short connector lead, while others have harness connected directly to unit.

When fuel level in tank is less than 3.0 gals. (11L), or fuel gauge is at or below fourth segment from bottom of display, this signals warning box around fuel gauge gas pump symbol to illuminate and flash at full intensity.

Warning system consists of an oil pressure switch and a warning light on instrument cluster. Oil pressure switch closes when oil pressure drops to less than 4 psi (.28 kg/cm 2 ) and illuminates warning light on instrument cluster. Oil pressure warning switch is mounted next to oil pressure sending unit on vehicles equipped with gauges. Warning switch is mounted in place of sending unit on vehicles NOT equipped with gauges. Light will illuminate when ignition is turned on, and if no problem exists, light will go out when engine starts.

If engine oil pressure drops to less than 10 psi (.70 kg/cm 2 ), oil pressure switch closes and signals warning box around oil pressure gauge oil can symbol to illuminate and flash at full intensity. Oil pressure warning switch is mounted next to oil pressure sending unit.

OIL PRESSURE GAUGE

Oil pressure gauge measures electrical current from variable-resistance oil pressure sending unit. Sending unit has low resistance when oil pressure is low and has about 90 ohms resistance when oil pressure is high. A change in resistance changes current flow through gauge electromagnetic coils, causing pointer to move from low to high.

Sending unit locations are as follows

1. 2.5L - In right side of block, under intake manifold.
2. 2.8L - At bottom left of engine block, on oil filter housing.
3. 4.3L - At top rear of engine block.

SERVICE ENGINE SOON OR CHECK ENGINE WARNING LIGHT

This warning light is part of computer command control system and will flash or stay on when a malfunction or trouble code(s) exists. Light will illuminate when ignition is turned on, and if no problem exists, light will go out when engine starts.

"S" & "T" Series (M/T)

This light shows when to upshift for best fuel economy at any acceleration. Disregard light during downshift. SHIFT light is controlled by ECM.

SPEEDOMETER/ODOMETER

Integrated circuits control the needle type air core speedometer and the stepper motor driven odometer. Speedometer/odometer receives its signals from the Digital Ratio Adapter Controller (DRAC), which receives its input signals from Vehicle Speed Sensor (VSS).

VEHICLE SPEED SENSOR

Vehicle Speed Sensor (VSS) is a permanent magnet signal generator located in transmission tailshaft housing. A toothed rotor or tone wheel fastened to transmission tailshaft rotates near VSS magnetic sensor coil, producing AC voltage pulses that are sent to the DRAC. This sensor assembly takes the place of speedometer cable and related gear hardware.

VOLTMETER

Voltmeter measures voltage of charging system with engine running and measures battery voltage with ignition on. Voltmeter uses an internal shunt. On electronic digital instrument clusters, if charging system malfunctions, signal box around voltmeter gauge battery symbol will illuminate and flash at full intensity.

BRAKE WARNING SYSTEM TESTING

If warning light does not illuminate when ignition switch is turned on, engine off and parking brake NOT applied, check for burned out light bulb. If bulb is okay, check for open in circuit by removing wire connector from differential pressure switch on brake combination valve and touch connector to ground. If warning light DOES NOT illuminate, repair open in circuit. If light does illuminate, circuit is okay. Replace differential pressure switch.

Light Inoperative

Turn ignition on. Check for burned out bulb and/or check for opens in printed circuit between oil pressure gauge and temperature gauge and between temperature gauge and CHECK GAGES light. If opens are found in printed circuit, replace instrument cluster. If printed circuit if okay, replace temperature gauge.

Light Inoperative With High Coolant Temperature

Check for inoperative coolant temperature gauge circuit, repair/replace temperature gauge/circuit as necessary. If temperature gauge circuit is okay, replace defective instrument cluster.

Light Inoperative With Low Oil Pressure

Check for inoperative oil pressure gauge/switch circuit, repair/replace as necessary. If gauge circuit is okay, replace defective instrument cluster.

Light Always On

Check for inoperative coolant temperature and oil pressure gauge circuits. Replace coolant temperature and/or oil pressure gauge if necessary. If coolant temperature and oil pressure gauge circuits are okay, replace defective instrument cluster.

COOLANT TEMPERATURE GAUGE (ASTRO & SAFARI) TESTING

Note. If vehicle is equipped with electronic coolant temperature gauge, see ELECTRONIC INSTRUMENT CLUSTER (ASTRO & SAFARI) .

Gauge Reads Cold When Engine Is Hot

1. Check for blown GAGE fuse. If fuse is okay, remove terminal connector from sending unit. Turn ignition on. Connect test light between sending unit harness connector and ground. If test light DOES NOT illuminate, go to step 3).
2. If test light illuminates and temperature gauge reads HOT, wiring circuit to gauge is okay. Check/repair sending unit lead connector. If wire lead and connector are okay, replace sending unit. If gauge still reads COLD, replace coolant temperature gauge.
3. With ignition off, ground sending unit harness connector and check continuity between sending unit terminal at gauge and ground and between gauge ignition terminal and ground. Also check temperature gauge case ground. If all checks are okay, replace coolant temperature gauge.

Gauge Reads Hot When Engine Is Cold

1. Turn ignition on. Disconnect terminal connector from temperature gauge sending unit. Gauge reading should go to COLD. If it does, replace sending unit.
2. If gauge continues to read HOT after replacing sending unit, check for short in wiring between sending unit and gauge. If no short is found, replace coolant temperature gauge.

Gauge Readings Are Inaccurate

1. Check wiring for corroded or loose connections. If necessary, clean and tighten terminals and connections. Also check for resistance in temperature sending unit ground circuit. If terminals, connections and ground circuit are okay, go to next step.
2. Disconnect lead from temperature gauge sending unit. Using ohmmeter, test sending unit resistance. See TEMPERATURE GAUGE SENDING UNIT RESISTANCE TABLE. If sending unit values are incorrect, replace sending unit.

TEMPERATURE GAUGE SENDING UNIT RESISTANCE

1. Check for blown GAGES fuse. If fuse is okay, disconnect connector from coolant temperature sending unit and turn ignition on. Connect test light from sending unit lead connector to ground. Gauge should read 260 (hot). If not, go to step 3).
2. If gauge reads 260, gauge is okay. Reconnect connector to sending unit. If gauge now reads 100, and engine is still hot, replace sending unit. If after replacing sending unit, gauge still reads near 100 with hot engine, gauge is also damaged and must be replaced.
3. If test light illuminates, circuit is okay. Replace gauge. If test light DOES NOT illuminate, connect test light to ignition terminal of gauge. If test light does illuminate, gauge is receiving voltage.
4. Connect test light to gauge sending unit terminal, gauge reading should go to 260. If not, gauge is defective. If gauge does go to hot, repair open in circuit between gauge and sending unit.

1. Turn ignition on. Remove connector from temperature gauge sensor. If gauge goes down to 100 (cold), replace externally shorted sending unit.
2. If temperature gauge continues to read 260, check for short to ground in wiring circuit between sending unit and gauge. If short is NOT found, replace temperature gauge.

1. Check wiring for corroded or loose connections. Clean and tighten terminals and connections as necessary. Also check resistance in temperature sending unit ground circuit. If terminals, connections and ground circuit are okay, go to next step.
2. Disconnect connector from temperature gauge sending unit. Using an ohmmeter, test sending unit resistance. See «TEMPERATURE GAUGE SENDING UNIT RESISTANCE TABLE»(/gmc/sonoma-syclone/1991-1992/remont/gauges-instrument-panels/#instrument-panel-except-syclone) . If sending unit values are incorrect, replace temperature gauge sending unit.

Warning Light Inoperative

If warning light does not come on during bulb check, check or replace burned out light bulb. If bulb is okay, check for an open in circuit. Remove terminal lead from coolant temperature switch and ground lead. If warning light does not come on, repair open in circuit. If light does come on, replace switch.

ELECTRONIC INSTRUMENT CLUSTER (ASTRO & SAFARI)

Note. Replace electronic instrument cluster if any one of the following conditions exists; Cluster display is always dim, speedometer is inoperative or inaccurate (odometer operating correctly), one or both odometers do not operate properly (speedometer operating correctly), low fuel indicator does not light with low fuel level, temperature indicator does not light with engine coolant overheated or oil pressure indicator does not light at all.

Scheme 1

1. Check ignition power to cluster, cluster ground and for an inoperative cluster. Disconnect large 17-pin connector from cluster.
2. Using a DVOM, measure voltage from harness connector pin terminal A13 to ground with ignition on. (Scheme 1) If battery voltage is present, go to next step. If DVOM reads less than battery voltage or zero, repair Black/White wire from ignition.
3. Turn ignition off. Using an ohmmeter, measure resistance from harness connector pin terminals A15 and A16 to ground. If ohmmeter reads anything but 0-0.5 ohm, repair Black wires at pin terminals A15 and A16 to ground. If resistance is correct, go to next step.
4. If ignition power feed and ground circuits are okay, replace inoperative instrument cluster.

Cluster Display Does Not Dim With Lights On

1. Check for open or shorted parking light power circuit, bad parking light switch and for an inoperative cluster. Turn parking lights and ignition on.
2. Using a DVOM, measure voltage between ground and pin terminal A8 of large 17-pin connector. If voltage reading is less than battery voltage, repair open or short in Brown wire. If voltage reading is okay, go to next step.
3. Using a DVOM, measure voltage between ground and pin terminal A8 of large 17-pin connector while adjusting panel light dimmer switch from high intensity to low intensity.
4. DVOM should read between zero and battery voltage. If not, repair Gray wire or replace parking light switch. If no problem is found, replace inoperative instrument cluster.

Cluster Display Does Not Switch Between English & Metric

1. Check for inoperative cluster control switch, wiring, or inoperative cluster. Disconnect large 17-pin connector at cluster. Measure cluster control switch resistance between connector pin terminal A2 and ground. (Scheme 1)
2. Resistance should be zero in one position and open in the other. If switch does not respond as indicated, repair Light Blue wire between cluster and switch, switch or Black wire from switch to ground.
3. If switch and related wiring are okay, replace inoperative instrument cluster.

Speedometer & Odometer Do Not Operate

1. Check for VSS signal. Disconnect large 17-pin connector from cluster and disconnect connector from Digital Ratio Adapter Controller (DRAC) that is mounted behind dash on bracket near radio.
2. Measure resistance of wire between connector pin terminal A1 of cluster connector and Light Blue/Black wire terminal of DRAC harness connector. If resistance is greater than zero ohms and the VSS circuit is working properly, replace inoperative instrument cluster.

Cluster Display Does Not Switch Between Total & Trip Odometer

1. Check for inoperative cluster control switch or wiring. Disconnect large 17-pin connector from cluster. Using an ohmmeter, measure resistance between cluster connector pin A3 and ground. (Scheme 1)
2. Resistance should be zero in one position and open in the other. If switch does not respond as indicated, repair Light Green wire between cluster and switch, or replace switch, or repair Black wire from switch to ground.
3. If switch and related wiring are okay, replace inoperative instrument cluster.

Trip Odometer Does Not Reset

1. Check for inoperative cluster control switch or wiring. Disconnect large 17-pin connector from cluster. Using an ohmmeter, measure resistance between cluster connector pin A5 and ground. (Scheme 1)
2. Resistance should be zero in one position and open in the other. If switch does not respond as indicated, repair Light Green/Black wire between cluster and switch, replace switch, or repair Black wire from switch to ground.
3. If switch and related wiring are okay, replace inoperative instrument cluster.

Fuel Gauge Is Inaccurate

1. Check for shorts or opens in wiring between fuel tank sending unit and cluster, or for an inoperative fuel tank sending unit. Disconnect fuel gauge sending unit at fuel tank. Connect one lead of Instrument Panel Tester (J-33431) to Pink wire and other lead to ground.
2. Turn ignition on. Set tester resistance dial to zero ohms. Fuel gauge should read empty. Now set resistance dial to 35 ohms. Fuel gauge should read half full or have 7-8 segments illuminated. Next, set resistance dial to 90 ohms. Fuel gauge should read full or fully illuminated (digital gauge).
3. If fuel gauge responds correctly to tester, check Black wire to ground at fuel gauge sending unit. If Black wire is okay, replace fuel gauge sending unit.
4. If gauge does not respond as indicated, check Pink wire between fuel gauge sending unit and cluster. If wire is okay, replace inoperative cluster.

Temperature Gauge Is Inaccurate

1. Check for shorts or opens in wiring between temperature sending unit and cluster, or for an inoperative temperature sending unit. Disconnect temperature sending unit at engine. Connect one lead of Instrument Panel Tester (J-33431) to Dark Green wire and other lead to ground.
2. Turn ignition on. Set tester resistance dials to 1400 ohms. Temperature gauge should read cold. Now set resistance dials to 400 ohms. Temperature gauge should read half or have 7-8 segments illuminated. Next, set resistance dials to zero ohms. Temperature gauge should read hot.
3. If temperature gauge responds correctly, replace temperature gauge sending unit. If gauge does not respond as indicated, check Dark Green wire between temperature gauge sending unit and cluster connector. If wire is okay, replace inoperative cluster.

Oil Pressure Gauge Inaccurate

1. Check for shorts or opens in wiring between oil pressure sending unit and cluster or for inoperative oil pressure sending unit. Disconnect oil pressure sending unit at engine. Connect one lead of Instrument Panel Tester (J-33431) to Tan wire and other lead to ground.
2. Turn ignition on. Set tester resistance dial to zero ohms. Oil pressure should read low. Now set resistance dial to 35 ohms. Oil pressure gauge should read half or have 7-8 segments illuminated. Set resistance dial to 90 ohms. Oil pressure gauge should read high.
3. If fuel gauge responds correctly, replace oil pressure gauge sending unit. If gauge does not respond as indicated, check Tan wire between fuel gauge sending unit and cluster connector. If wire is okay, replace inoperative cluster.

Voltmeter Is Inaccurate

1. Check for short, open, or high resistance between alternator Brown wire and cluster. Using a DVOM, measure voltage between battery terminals and measure voltage between Brown wire and ground.
2. If readings are different, repair Brown wire. If readings are the same, check Black ground wire for high resistance to ground. If Black wire is okay, replace inoperative instrument cluster.

ELECTRONIC INSTRUMENT CLUSTER ("S" & "T" SERIES) TESTING

Note. Replace electronic instrument cluster if any one of the following conditions exists; Cluster display is always dim, speedometer is inoperative or inaccurate (odometer operating correctly), one or both odometers do not operate properly (speedometer operating correctly), low fuel indicator does not light with low fuel level, temperature indicator does not light with engine coolant overheated or oil pressure indicator does not light at all.

Cluster Display Does Not Light

1. Check ignition feed to cluster. Disconnect 34-pin connector from cluster. Using a voltmeter, measure voltage between instrument cluster connector terminal A15 and ground with ignition on. (Scheme 1)
2. If battery voltage is not present, repair open in Pink/Black wire from ignition. If battery voltage is present, measure voltage between instrument cluster connector terminals A15 and B7.
3. If battery voltage is present, replace cluster. If battery voltage is not present, repair open in Black wire between ground and instrument cluster connector B7.

1. Disconnect 34-pin connector from cluster. Using a voltmeter, measure voltage between instrument cluster connector terminal A6 and ground with ignition and parking lights on. (Scheme 1)
2. If reading is less than battery voltage, repair open or short in Brown wire to instrument cluster connector terminal A6. If battery voltage is present, go to next step.
3. While still measuring voltage between terminal A6 and ground, adjust instrument panel light dimmer switch from high intensity to low intensity. If voltage does not drop as switch is turned from high to low intensity, check Brown wire between instrument cluster connector terminal A6 and park light switch. Repair as necessary.
4. If Brown wire is okay, check park light switch. Replace as necessary. If park light switch is okay, replace instrument cluster.

Speedometer & Odometers Do Not Operate

1. Disconnect 34-pin connector from cluster. Disconnect Digital Ratio Adapter Controller (DRAC) connector. Using an ohmmeter, measure resistance between terminal A11 of instrument cluster connector and Light Blue/Black wire terminal of DRAC connector. (Scheme 1)
2. If resistance is greater than zero ohms, check vehicle speed sensor and ensure correct DRAC is installed. See VEHICLE SPEED SENSOR & DIGITAL RATIO ADAPTER CONTROLLER (DRAC) TESTING. If vehicle speed sensor and DRAC are okay, replace instrument cluster.

1. Disconnect fuel gauge sending unit at fuel tank. Connect one lead of Signal Generator & Instrument Panel Tester (J-33431) to Pink wire of sending unit connector and other lead to ground. Turn ignition on and adjust resistance dials of tester to different settings and check fuel gauge. See FUEL GAUGE SENDER RESISTANCE SPECIFICATIONS TABLE. FUEL GAUGE SENDER RESISTANCE SPECIFICATIONS Resistance Setting Fuel Gauge Reading Zero Ohms Empty 35 Ohms Half Full (7-8 Segments Lit) 90 Ohms Full
2. If fuel gauge responds correctly, check Black (ground) wire from fuel sending unit and repair as necessary. If Black wire is okay, replace fuel tank sending unit.
3. If fuel gauge does not respond correctly, check Pink wire between fuel sending unit and instrument cluster connector terminal A12. (Scheme 1) Repair as necessary. If Pink wire is okay, replace instrument cluster.

1. Disconnect temperature sending unit and connect one lead of Signal Generator & Instrument Panel Tester (J-33431) to Dark Green wire of temperature sending unit connector and other lead to ground. Turn ignition on and adjust resistance dials of tester to different settings and check temperature gauge. See TEMPERATURE GAUGE SENDER RESISTANCE SPECIFICATIONS TABLE. TEMPERATURE GAUGE SENDER RESISTANCE SPECS Resistance Setting Temperature Gauge Reading 1400 Ohms Cold 400 Ohms Warm (7-8 Segments Lit) 55 Ohms Hot
2. If gauge responds correctly, replace temperature sending unit. If gauge does not respond correctly, check Dark Green wire between temperature sending unit and instrument cluster connector terminal A1. (Scheme 1) Repair as necessary. If Dark Green wire is okay, replace instrument cluster.

Oil Pressure Gauge Is Inaccurate

1. Disconnect oil pressure sending unit and connect one lead of Signal Generator & Instrument Panel Tester (J-33431) to Tan wire of oil pressure sending unit connector and other lead to ground. Turn ignition on and adjust resistance dials of tester to different settings and check oil pressure gauge. See OIL PRESSURE GAUGE SENDER RESISTANCE SPECIFICATIONS TABLE. OIL PRESSURE GAUGE SENDER RESISTANCE SPECS Resistance Setting Oil Pressure Gauge Reading Zero Ohms Low 35 Ohms Half (7-8 Segments Lit) 90 Ohms High
2. If gauge responds correctly, replace oil pressure sending unit. If gauge does not respond correctly, check Tan wire between oil pressure sending unit and instrument cluster connector terminal A2. (Scheme 1) Repair as necessary. If Tan wire is okay, replace instrument cluster.

1. Measure and record voltage between battery terminals. Disconnect 34-pin instrument cluster connector. Measure voltage between instrument cluster connector terminal A15 and chassis ground. (Scheme 1) If voltage readings are different, repair Pink/Black wire from instrument cluster connector terminal A15. If voltage readings are the same, go to next step.
2. Using an ohmmeter, measure resistance between ground and instrument cluster terminals A9 and B7. If high resistance is present in either circuit, repair open or short in appropriate Black wire. If wires are okay, replace instrument cluster.

FUEL GAUGE TESTING

Note. If vehicle is equipped with electronic fuel gauge, see appropriate ELECTRONIC INSTRUMENT CLUSTER TESTING.

Gauge Stays At Empty Position

Check for fuel in tank. Turn ignition on. Check for a grounded fuel gauge circuit by disconnecting lead at fuel tank. Fuel gauge should now read past FULL mark. If gauge does not read past FULL mark, replace fuel gauge sending unit in tank. If gauge still reads EMPTY, repair short to ground between gauge and fuel tank.

Gauge Stays At Full Position

1. Turn ignition on. Check for open circuit between gauge and sending unit by disconnecting sending unit lead at fuel tank. Jumper wire sending unit lead to ground and note gauge reading.
2. If fuel gauge now reads EMPTY, replace fuel gauge sending unit. If fuel gauge still reads FULL or beyond, repair open in wire between gauge and fuel tank.

Gauge Reading Is Inaccurate

1. Check wiring for corroded or loose connections. Clean and tighten as required. If wiring and connections are okay, remove fuel gauge sending unit. Using an ohmmeter, test sending unit resistance. See «FUEL GAUGE SENDING UNIT RESISTANCE TABLE»(/gmc/sonoma-syclone/1991-1992/remont/gauges-instrument-panels/#instrument-panel-except-syclone) .
2. If sending unit values are correct, disconnect front body wiring harness connector at engine firewall. Connect Gauge Tester (J-24538-A) to terminal No. 30 (Purple wire). Turn ignition on. If gauge reads accurately when connected to Gauge Tester, check wiring between fuel tank and front connector.
3. If gauge reads between 1/4 and 1/2 full with tester set at 90 ohms, replace fuel gauge.

FUEL GAUGE SENDING UNIT RESISTANCE

OIL PRESSURE GAUGE TESTING

Note. If vehicle is equipped with electronic oil pressure gauge, see appropriate ELECTRONIC INSTRUMENT CLUSTER TESTING.

Gauge Reads "0" With Engine Running

1. Check oil level and add if necessary. Test oil pressure with manual gauge and adapter. If oil pressure reading is good on manual gauge tester, check for grounded gauge circuit by disconnecting lead at sending unit.
2. Turn ignition on. Oil pressure gauge should now read 80. If gauge stays at zero, disconnect lead from gauge. Gauge should now read 80. If gauge reads 80, find short to ground between gauge and sending unit. If gauge still reads zero, replace gauge and test oil pressure gauge sending unit resistance. See «OIL PRESSURE GAUGE SENDING UNIT RESISTANCE TABLE»(/gmc/sonoma-syclone/1991-1992/remont/gauges-instrument-panels/#instrument-panel-except-syclone) . Replace sending unit if it reads one ohm with engine running.

Gauge Constantly Reads 80 Or More

1. Check for open circuit between gauge and sending unit by disconnecting lead at sending unit. Connect lead to ground and note reading on gauge.
2. If oil pressure gauge reads zero, replace oil pressure gauge sending unit. If oil pressure gauge still reads 80 or more, find open wire between gauge and sending unit.

Disconnect lead from oil pressure sending unit. Connect Gauge Tester (J-24538-A) for Astro and Safari or (J-33431) for "S" & "T" Series to lead and ground. Turn ignition on. If gauge reads accurately, replace oil pressure sending unit. If gauge still reads inaccurately, replace oil pressure gauge.

OIL PRESSURE GAUGE SENDING UNIT RESISTANCE

OIL PRESSURE WARNING SYSTEM TESTING

Turn ignition on. If warning light does not come on, check for burned-out bulb. If bulb is okay, check for an open in warning switch circuit (NOT same circuit as sending unit). Remove lead connector from oil pressure switch and connect to ground. If warning light DOES NOT come on, find open in circuit. If light does come on, replace warning switch.

Speedometer & Odometer Are Inaccurate

Ensure that correct digital ratio adapter controller is installed for specific final drive ratio. Replace if necessary.

Speedometer & Odometer Do Not Operate Properly

1. Disconnect Digital Ratio Adapter Controller (DRAC). Turn ignition on. Measure voltage between Pink/Black wire of DRAC harness connector and good chassis ground.
2. If battery voltage is present, go to next step. If voltage is less than battery voltage, check for blown BRAKE fuse and replace if necessary. If fuse is okay, check for an open or short in Pink/Black wire between fuse block and DRAC harness connector. Repair as necessary.
3. On Astro and Safari, measure voltage between Pink/Black wire terminal and Black/White wire terminal of DRAC harness connector. If battery voltage is present, go to step 5). If battery voltage is not present, check for open or short in Black/White wire and repair as necessary.
4. On "S" and "T" Series, measure voltage between Light Blue/Black wire terminal and Black wire terminal of DRAC harness connector. If battery voltage is present, go to next step. If battery voltage is not present, check for open or short in Black wire and repair as necessary.
5. Raise and support vehicle. Start engine and place transmission in Drive. Measure voltage between Purple/White wire terminal and Light Green/Black wire terminal of DRAC harness connector.
6. If voltage is present, go to next step. If voltage is not present, check both wires for shorts or opens and repair as necessary. If wires are okay, replace vehicle speed sensor.
7. With vehicle still raised, engine running and transmission in Drive, connect DRAC harness connector to digital ratio adapter controller. Backprobe DRAC harness connector and measure voltage changes between Pink/Black wire terminal (Light Blue/Black wire terminal on "S" and "T" Series) and Black/White wire terminal (Black wire terminal on "S" and "T" Series) while varying vehicle speed.
8. If voltage does not change with vehicle speed, go to next step. If voltage varies with vehicle speed, replace DRAC.
9. Measure voltage between DRAC harness connector Yellow wire terminal and Black/White wire terminal (Black wire terminal on "S" and "T" Series) while varying vehicle speed.
10. If voltage does not vary with vehicle speed, test instrument cluster. See appropriate ELECTRONIC INSTRUMENT CLUSTER TESTING. If voltage varies with vehicle speed, replace DRAC.

VOLTMETER TESTING

Note. If vehicle is equipped with electronic voltmeter, see appropriate ELECTRONIC INSTRUMENT CLUSTER TESTING.

1. Measure voltage across battery terminals. Voltage should be approximately 12 volts. If battery is discharged, recharge battery and perform load test. Repair cause of discharged battery.
2. With ignition on and battery terminals cleaned and connected, observe voltmeter with battery charger in operation. Voltmeter should read 12 volts or more. If not, check for high resistance in voltmeter terminal connections. Clean and tighten connections.
3. If voltmeter reading is still low, apply 12 volts directly to positive terminal of voltmeter. If voltmeter does not respond accurately, replace voltmeter.

Disconnect negative battery cable. Unplug instrument panel harness from DRAC. See DRAC LOCATIONS TABLE. To install, reverse removal procedure.

DRAC LOCATIONS

GAUGES

Note. If vehicle is equipped with electronic gauges, instrument cluster is NOT serviceable and is to be replaced as complete assembly. See INSTRUMENT CLUSTER under REMOVAL & INSTALLATION.

Removal & Installation (Astro & Safari)

Remove instrument cluster. See INSTRUMENT CLUSTER under REMOVAL & INSTALLATION. Remove cluster case retainer screws and retainer (if equipped). Remove individual gauge mounting screws. Carefully remove gauge. (Scheme 2) To install, reverse removal procedure.

Scheme 2

1. Disconnect negative battery terminal. Remove instrument cluster trim plate screws. (Scheme 2) Remove lower steering column trim plate and instrument cluster trim plate.
2. Remove instrument cluster screws. Touch hands to ground to discharge static electricity before pulling out cluster to disconnect instrument cluster harness and speedometer cable. Remove instrument cluster. To install, reverse removal procedure.

Removal & Installation ("S" & "T" Series)

1. Disconnect negative battery terminal. Remove light switch trim plate and disconnect light switch harness. Remove A/C-heater control assembly and disconnect A/C-heater control assembly harness.
2. Remove filler panel (lower steering column panel). (Scheme 3) Remove instrument cluster housing nuts and cluster. Touch hands to ground to discharge static electricity before pulling out instrument cluster to disconnect harness connections and remove cluster. To install, reverse removal procedure.

Scheme 3

Remove instrument cluster. See INSTRUMENT CLUSTER under REMOVAL & INSTALLATION. Remove lens screws, lens, faceplate/applique and retainer. Remove speedometer retaining screws and speedometer. (Scheme 2) To install, reverse removal procedure.

Disconnect negative battery terminal. Remove instrument cluster. See INSTRUMENT CLUSTER under REMOVAL & INSTALLATION. Disconnect instrument cluster harness from trip switch panel. Remove screws and trip switch panel. To install, reverse removal procedure.

Removal & Installation

Raise and support vehicle. Unplug vehicle speed sensor harness at transmission tailshaft housing. Remove hold-down bolt, or unscrew vehicle speed sensor. Catch transmission fluid in a container. Remove "O" ring. To install, reverse removal procedure and recheck fluid level.

See also:
• CHECK GAUGES LIGHT DESCRIPTION
• ELECTRONIC INSTRUMENT CLUSTER (ASTRO & SAFARI)