The Nissan Diesel D21 (also known as the Datsun Truck or Navara) is a rugged diesel pickup from the 1980s-1990s. Its instrument cluster is simple but vital for monitoring engine health, featuring basic warning lights for key systems like charging, oil pressure, and preheat.
Nissan Diesel D21 Warning Light Symbols
| Symbol | Name | Color | What it means | What to do |
|---|---|---|---|---|
| Check Engine (MIL) | AMBER | For D21's SD25 or TD27 diesel, this light may indicate a faulty injection pump timing sensor, air in fuel, or a glow plug relay issue. | Check for loose fuel lines or water in the separator; if persistent, have a diesel shop test the injection pump. | |
| Oil Pressure Warning | RED | Oil pressure drop in the D21's diesel engine often signals low oil level, a clogged oil screen, or a failing oil pump. | Immediately stop and check oil level; if OK, do not restart – tow to a mechanic for oil pressure test. | |
| Battery / Charging | RED | With the D21's alternator rated at 55-60 amps, this light indicates a failed alternator, broken belt, or a dead cell in the battery. | Check alternator belt tension; if loose, tighten; if light stays on, have charging system tested. | |
| Coolant Temperature | RED | Overheating in the D21 can be caused by a stuck thermostat, fan clutch failure, or debris blocking the radiator on dusty job sites. | Pull over, let engine idle with heater on full; check coolant level after cooling. | |
| Brake System Warning | RED | On the D21, this light often means low brake fluid due to worn pads or a leak in a wheel cylinder or lines. | Check brake fluid reservoir; if low, inspect for leaks and top up with DOT 3 or 4 fluid. | |
| Parking Brake Indicator | RED | The light stays on in the D21 if the parking brake is engaged or the switch is stuck – common after rust or debris on the pedal linkage. | Release parking brake fully; if light stays, check the switch near the pedal pivot. | |
| Seat Belt Reminder | RED | The D21's seatbelt light is tied to a timer that flashes for about 8 seconds if the driver's belt is not buckled. | Fasten your seatbelt to extinguish the light. | |
| Glow Plug / Preheat | AMBER | In the D21's cold-start system, this light stays on while the glow plugs heat; a fast-flashing light indicates a faulty glow plug or relay. | Wait for the light to go out before cranking; if flashing, test glow plugs with a multimeter. | |
| Water in Fuel | AMBER | The D21's fuel filter/water separator has a sensor that triggers this light when water accumulates – common after running low-quality diesel. | Drain the water separator (located under the fuel filter) by opening the drain valve until clear fuel flows. | |
| Low Fuel | AMBER | This light warns that the D21's fuel level is below about 8 liters (2 gallons) – it's a mechanical pickup, so running dry can damage the injection pump. | Refuel with diesel ASAP; do not rely on reserve. | |
| High Beam Indicator | BLUE | The blue high beam light comes on when the high beams are active via the stalk on the D21's steering column. | No action needed; dim your lights for oncoming traffic. | |
| Door Open | RED | In cab-and-chassis D21 models, this light indicates a open door – the switch can fail due to worn plunger or dirt. | Close all doors securely; if light stays, clean door switch contacts. |
12 symbols shown. Icons follow ISO 2575 dashboard standards; exact graphics vary by model year.
Most Important Warning Lights
Low Oil Pressure
Common causes
- Oil level too low
- Clogged oil pickup screen
- Worn oil pump or main bearings
What to do
For D21, first check oil dipstick; if OK, suspect screen clogging from sludge. Drop oil pan to clean screen and replace oil pump if worn.
Overheated Engine
Common causes
- Thermostat stuck closed
- Fan clutch not engaging
- Radiator fins blocked with mud or grass
What to do
Replace thermostat (common failure on D21). Check fan clutch freeplay; if loose, replace. Pressure wash radiator externally.
Alternator Failure
Common causes
- Failed voltage regulator (built-in alternator)
- Broken or loose V-belt
- Worn brushes or slip rings
What to do
Test alternator output at battery (13.5-14.5V). Replace alternator if output low; D21 uses Hitachi or Mitsubishi units – upgrade to higher amp if needed.
Brake Fluid Loss
Common causes
- Worn brake pads/shoes
- Leaking wheel cylinder
- Cracked brake line
What to do
Inspect all wheel cylinders for wetness; if leaking, rebuild or replace. Replace brake lines if rusted. Always bleed system after repair.
Glow Plug System Fault
Common causes
- Burnt-out glow plug(s)
- Failed glow plug relay
- Corroded wiring connections
What to do
Test each glow plug resistance (0.5-2 ohms). Replace in sets of four. Clean relay contacts; D21 relay is underhood near battery.
Frequently Asked Questions
Why does my D21's check engine light come on after refueling?
Often the water-in-fuel sensor triggers if you picked up contaminated diesel. Drain the water separator and it may reset; if still on, check for air leaks in the fuel line.
The glow plug light blinks rapidly – can I still start?
Fast blinking usually means one or more glow plugs are faulty. The engine may start hard in cold weather. Replace all glow plugs to ensure proper preheating.
My brake warning light stays on even with full fluid. What's wrong?
On D21, the light has a pressure differential switch. A brake circuit leak (front vs rear) can cause an imbalance. Check for internal leaks in master cylinder or wheel cylinders.
How do I reset the parking brake light if it won't turn off?
Manually release the pedal. If light stays, locate the switch on the parking brake pedal assembly – adjust or replace the switch if it's shorted due to rust.
The battery light flickers at idle – is that normal?
Not normal – indicates the alternator is not charging enough at low RPM. Clean battery terminals and check belt tension. D21's alternator may need a new voltage regulator.
My D21 has a water-in-fuel light but the separator drains clear fuel. What's up?
The sensor may be faulty or the wiring has a short. Unplug the sensor connector – if light goes off, replace the sensor. If not, check for chafed wires near the fuel filter.