DIAGNOSTIC GUIDES
Common diesel problems & what they mean.
Low power, hard starts, smoke or a warning light? Pick a symptom to see what usually causes it on your engine, and why we test before replacing parts.
- 15common problems
- 3diesel platforms
- Test firstthen repair
- Mobilewe come to you
What’s your truck doing?
DIAGNOSTIC GUIDE · FORD POWER STROKE
Ford Power Stroke.
Possible causes, not a diagnosis. The repair depends on model year, configuration and test results.
- Oil vs. coolant temp
6.0L oil cooler & cooling
Rising oil temps, coolant loss or overheating can point to a restricted oil cooler, EGR cooler or cooling faults.
Overheating / coolant lossWarning light / derateAsk about diagnosis → - P0611 · ICP faults
6.0L hard starts & high-pressure oil
Long cranking or hot no-starts can be high-pressure oil leaks, injection-pressure control or FICM voltage.
Hard start / no startWarning light / derateAsk about diagnosis → - P0087 · P0093
6.7L fuel pressure & CP4
No-start, low rail pressure or stumbling needs supply, contamination and pump checks. Metal debris changes the whole repair.
Hard start / no startLow powerWarning light / derateAsk about diagnosis → - P0299 · P0046
Underboost & VGT
A low-boost code doesn’t prove a bad turbo. Charge-air leaks, exhaust leaks, sensors and the actuator are checked first.
Low powerNoise / whistleWarning light / derateAsk about diagnosis → - P0340 · contribution
7.3L / 6.0L injectors & sensors
Rough running, smoke or stalling on older Power Strokes: cam sensor, IDM/FICM and injector health.
Hard start / no startSmokeLow powerAsk about diagnosis →
Specs, codes and generation details: Ford Power Stroke field guide →
DIAGNOSTIC GUIDE · RAM CUMMINS
Ram Cummins.
Possible causes, not a diagnosis. The repair depends on model year, configuration and test results.
- P2262 · P0299
6.7L VGT turbo & actuator
Low power, weak exhaust brake or boost faults often come from a sticking VGT or failing actuator.
Low powerWarning light / derateNoise / whistleAsk about diagnosis → - P0087 · P0088
Fuel rail pressure & hard starts
Long cranking, stalling or rail-pressure codes can start at a restricted filter, weak lift pump, pressure control, injectors or CP3.
Hard start / no startLow powerWarning light / derateAsk about diagnosis → - P0540 · grid heater
Grid-heater hardware
Some 6.7L engines have known grid-heater bolt concerns. Inspect and secure before parts end up in the engine.
Warning light / derateHard start / no startAsk about diagnosis → - P2463 · P20EE
DPF, DEF & derate
Emissions warnings can be sensors, wiring, DEF dosing, exhaust leaks or soot loading. Fix the cause before a regen.
Warning light / derateLow powerSmokeAsk about diagnosis → - VP44 · KDP
5.9L KDP & lift pump
On 12v and 24v trucks, a backing-out dowel pin and a weak lift pump cause expensive damage.
Noise / whistleHard start / no startLow powerAsk about diagnosis →
Specs, codes and generation details: Ram Cummins field guide → · Every 2003–2007 5.9 weak point, system by system: 3rd-gen 5.9 repair guide →
DIAGNOSTIC GUIDE · CHEVY / GMC DURAMAX
Chevy / GMC Duramax.
Possible causes, not a diagnosis. The repair depends on model year, configuration and test results.
- P0087 · P0089
LML CP4 fuel-system failures
Hard starts, power loss or contamination: supply pressure, filters and pump condition. Pump debris reaches the injectors.
Hard start / no startLow powerWarning light / derateAsk about diagnosis → - Balance rates
LB7 injectors & return flow
Rough running, smoke, hard starts or fuel in the oil call for balance-rate and return-flow testing, not a parts swap.
SmokeHard start / no startLow powerAsk about diagnosis → - P20EE · P2002
L5P fuel & emissions faults
Newer L5P complaints can be fuel delivery, controls, NOx sensors, DEF or aftertreatment.
Warning light / derateLow powerAsk about diagnosis → - P0299 · P0236
Boost leaks & turbo
Whistling, low power or underboost: intercooler boots, resonator, clamps, sensors or turbo controls.
Noise / whistleLow powerWarning light / derateAsk about diagnosis → - P0218 · trans temp
Allison trans heat & shifting
Towing in the heat pushes Allison temps up; slipping or harsh shifts follow.
Overheating / coolant lossWarning light / derateAsk about diagnosis →
Specs, codes and generation details: Chevy / GMC Duramax field guide →
CODES
Common diesel trouble codes.
| Code | Meaning |
|---|---|
| P0087 | Fuel rail pressure too low |
| P0088 | Fuel rail pressure too high |
| P0093 | Fuel system large leak |
| P0299 | Turbo underboost |
| P2262 | Boost pressure not detected |
| P0401 | EGR flow insufficient |
| P2463 | DPF soot accumulation |
| P20EE | SCR NOx efficiency low |
| P0611 | Fuel injector control module |
| P0670 | Glow plug control module |
A code tells us which system to test, not which part to buy. See how we diagnose.
BEFORE YOU CALL
What to have ready.
The more we know, the faster we can find it.
Year, make, model, engine
Or the VIN from the dash or door jamb.
Mileage & how it’s used
Towing, daily, fleet, idling, mods or tune.
Symptoms
When it happens: cold, hot, under load, at idle.
Fault codes
Photo of the dash or a scan readout if you have one.
Recent repairs
Anything replaced lately, even if it seemed unrelated.
Where the truck is
Address and access, so we bring the right equipment.
Emissions services are performed in accordance with applicable laws.
QUESTIONS
Diagnosis FAQ.
Can you just replace the part the code points to?
We can, but a code points to a system, not a part. Testing first usually saves money: many “bad turbo” or “bad pump” codes turn out to be a leak, a filter or a sensor.
Can you diagnose it at my location?
Yes. We bring scan tools, pressure gauges and smoke testers to your driveway, job site or yard across Tucson.
My truck is in limp mode. Is it safe to drive?
Derate protects the engine. Short, gentle trips are usually OK, but towing or long drives can make it worse. Call us and we’ll tell you if it should stay put.
What do you charge?
Labor is $149–$298/hour by truck class, and you approve a written estimate before repairs. See rates.
READY WHEN YOU ARE
Stop guessing. Let’s find the cause.
Tell us the symptoms and any codes. We’ll bring the right tools to your truck.