Common Truck Problems

Symptoms

• •Engine cranks but won't fire
• •No crank at all
• •Starts briefly then dies

Common Causes

• •Dead or weak batteries
• •Fuel system air leak or low fuel pressure
• •Failed fuel lift pump
• •Bad crankshaft position sensor
• •ECM power or ground fault

First Steps

1. 1.Check battery voltage (should be 12.6V+ per battery)
2. 2.Check for active fault codes before cranking
3. 3.Verify fuel pressure at the lift pump outlet
4. 4.Check ECM power and ground fuses

Symptoms

• •Loss of power under load
• •Slow acceleration
• •Can't maintain highway speed
• •Black smoke under load

Common Causes

• •Clogged DPF (high backpressure)
• •Turbo not building boost
• •Fuel restriction or clogged fuel filter
• •EGR valve stuck open
• •Derate active from fault codes

First Steps

1. 1.Check for active fault codes and derates
2. 2.Check DPF backpressure (delta-P sensor data)
3. 3.Check boost pressure in live data
4. 4.Inspect air filter and intake restriction

Symptoms

• •Low boost pressure in live data
• •Slow spool-up
• •Black smoke
• •Power loss under load

Common Causes

• •Boost leak in charge air system
• •VGT actuator failure
• •Turbo wheel damage
• •EGR cooler leak reducing exhaust flow
• •Turbo speed sensor fault

First Steps

1. 1.Check boost pressure in live data vs. expected
2. 2.Inspect charge air cooler and all boost hoses for leaks
3. 3.Check VGT actuator response in live data
4. 4.Look for turbo-related fault codes (SPN 102, 1127, 641)

Symptoms

• •DPF warning light on
• •Regen inhibited
• •Forced regen fails
• •High DPF soot load in live data

Common Causes

• •Faulty DPF differential pressure sensor
• •Failed DOC (diesel oxidation catalyst)
• •Low exhaust temps from short trips
• •DEF system fault preventing regen
• •Coolant or oil contamination in DPF

First Steps

1. 1.Check DPF delta-P sensor and hoses for blockage
2. 2.Check DOC inlet/outlet temperature differential
3. 3.Verify no active derates blocking regen
4. 4.Attempt a parked forced regen and monitor temps

Symptoms

• •DEF warning light or message
• •SCR efficiency fault codes
• •Derate active or approaching

Common Causes

• •Low DEF level
• •Contaminated DEF (wrong fluid added)
• •Failed DEF injector
• •Faulty NOx sensor (upstream or downstream)
• •SCR catalyst degraded

First Steps

1. 1.Check DEF level and quality (should be clear, not yellow)
2. 2.Check for NOx sensor fault codes (SPN 3226, 3227, 3251)
3. 3.Verify DEF injector is not clogged
4. 4.Check DEF quality sensor reading in live data

Symptoms

• •Uneven idle
• •Engine shaking at idle
• •RPM hunting
• •Misfires at idle

Common Causes

• •Faulty injector (stuck open or closed)
• •Air in fuel system
• •EGR valve stuck open at idle
• •Low fuel pressure
• •Cylinder contribution fault

First Steps

1. 1.Check for injector-related fault codes
2. 2.Run cylinder contribution test if available
3. 3.Check fuel pressure at idle
4. 4.Inspect EGR valve operation in live data

Symptoms

• •Low fuel rail pressure fault codes
• •Hard start
• •Power loss
• •Engine stalling

Common Causes

• •Clogged fuel filter
• •Failing fuel lift pump
• •Leaking fuel pressure regulator
• •Cracked fuel line or fitting
• •High-pressure pump wear

First Steps

1. 1.Replace fuel filter (most common cause)
2. 2.Check lift pump pressure at the outlet
3. 3.Check for fuel rail pressure fault codes (SPN 94, 157)
4. 4.Inspect fuel lines for cracks or leaks