FAQ – Quick Questions about IQA Code

Q1: What is an IQA code?
An IQA (Injector Quantity Adjustment) code is a unique correction value used to fine-tune the fuel injection quantity of each diesel injector. It helps the ECU compensate for manufacturing differences to improve engine performance and emissions.

Q2: Why do injectors need IQA correction?
No two injectors are exactly the same due to machining variations. IQA codes correct these differences to ensure balanced fuel injection among cylinders.

Q3: When should IQA codes be programmed?
IQA codes should be programmed after replacing the ECU, replacing injectors, or adjusting the injector sequence.

Q4: What happens if the IQA code is not programmed?
Possible engine issues include increased fuel consumption, engine shaking, warning lights, knocking, black smoke, and reduced power.

Explanation of Injector Fuel Quantity Correction – IQA Code

In a strict sense, there are no two identical things in the world. Even identical twins are only visually similar, not 100% identical, just like how no two leaves are exactly the same. The same principle applies to injectors: no two injectors are identical, even with the most advanced manufacturing technology and precise equipment.

During mass production, injectors have deviations due to inconsistent machining accuracy, such as differences in spray diameter, orifice size, and solenoid valves. After use or maintenance, their actual fuel injection quantity may also differ from the theoretical standard. This leads to discrepancies in fuel injection quantity among cylinders when installed in an engine, causing errors in engine performance and emission consistency.

To address this, injector manufacturers use IQA (Injector Quantity Adjustment) technology, which corrects the fuel quantity of each injector to improve injection accuracy and unify the injection characteristics of mass-produced injectors. This essentially uses software to compensate for hardware manufacturing errors.

I. Schematic Positions of Common Injector QR Codes

Injector correction codes have different names in various systems, such as IQA code, IMA code, QR code, correction code, or bar code.

Bosch Injector IQA Code

The Bosch IQA code consists of 7 digits, a mix of uppercase letters (excluding J and Q) and numbers (excluding 0 and 9). It is a compensation code generated from fuel quantity differences across five working conditions, input into the ECU to correct variations between injectors in a common rail system, making the fuel quantity-injection time MAP closer to the standard.

Example:
An injector model 0445110677 with IQA code AART1S8:

• 1st digit: Emission point fuel compensation
• 2nd digit: Idle speed point
• 3rd digit: Full load point
• 4th digit: Pre-injection 1 point
• 5th–6th digits: Checksum and quantization threshold
• 7th digit: Pre-injection 2 fuel compensation (for piezoelectric injectors, it is the ISA voltage correction value)

Bosch’s IQA code is simpler to generate, requiring only fuel quantity differences from conventional test conditions and an algorithm. However, accurate test bench results (close to OEM equipment) are essential, as incorrect data can worsen maintenance issues.

Cummins Injector Bar Code

Unlike Bosch, the Cummins correction code excludes letters “I” and “O” but includes numbers “1” and “0” (care should be taken to distinguish them).

Delphi Injector Correction Code

• EJBR03301D injectors: 16-digit code
• EJRB05301D injectors: 20-digit code, divided into C2i and C3i by algorithm
• Some injectors: 8-digit code

Denso Injector QR Code

Common QR codes include 16, 24, 30, and 32 digits (30-digit codes for Denso 6222 injectors are most typical). The code contains information such as part numbers, manufacturing numbers, engine models, fuel injection correction, and response time correction, uniquely identifying each injector.

Compared to Bosch’s IQA code, Denso’s QR code refines fuel correction across more than ten working conditions, calculates correction percentages, and matches injection response time. Inaccurate response time matching can cause idle instability and engine shaking.

II. Principle and Activation of IQA Fuel Quantity Correction

The ECU controls injector fuel injection by supplying current, with the power-on time (injection duration) being critical. The IQA code modifies this duration to correct fuel quantity:

• For injectors with larger flow rates, the adjustment is negative
• For injectors with smaller flow rates, the adjustment is positive

Final power-on time = initial power-on time + adjustment value

Unlike adjusting internal shims, QR codes fine-tune injection quantity by changing electrical signal duration, balancing fuel injection among cylinders.

III. Impact of Unprogrammed IQA Code on the Engine

• Increased fuel consumption
• Malfunction indicator light activation
• Engine shaking
• Engine knocking
• Black smoke emission
• Reduced engine power

IV. When to Program IQA Code

• Replacing the ECU
• Replacing the injector
• Adjusting injector sequence

V. Impact of IQA on Engine Emissions

Without IQA:
Injectors with maximum flow require less power-on time than the median (standard) injector, resulting in shorter combustion time and lower NOx; minimum flow injectors show the opposite.

With IQA:
Maximum flow injectors are corrected to shorter power-on times, increasing rail pressure and main injection timing, which raises NOx. Minimum flow injectors see reduced rail pressure and main injection, lowering NOx.

IQA also corrects engine power in external characteristics.

VI. Why Do Some Large-Displacement Engines Lack IQA Codes?

Large-displacement engines have high base fuel injection quantities, making QR code corrections relatively insignificant. In contrast, small-displacement engines have lower base quantities, so uncorrected IQA codes would cause abnormal engine operation due to more pronounced correction ratios.