TDI injector corrections in VCDS: groups 013, 018 and 023

Updated: 2026-11-03

Your TDI shakes at idle and you want to know which injector is to blame. VCDS shows it in three measuring groups: 013 (how much fuel the control unit adds to or takes from each cylinder), 018 (the status of the unit injectors) and 023 (their switch time deviation). This guide shows how to read them on 1.9 and 2.0 TDI engines with a distributor pump (VE) and with unit injectors (PD). A section on common rail TDIs is at the end.

If you do not have a log yet, start with How to record a VCDS log. Unlike a boost log, this one needs no driving: the values are read at idle, with the car standing still.

In short: what a healthy log looks like

• Warm engine, idle: every cylinder in group 013 stays within the specified range, ±2.0 mg on most VE engines and ±2.8 mg on PD engines. Values close to zero, within about ±1 mg, are the best case.
• The values add up to about zero. If one cylinder is far off, the others move the opposite way.
• Group 018 (PD only) shows 0 in every field.
• Group 023 (PD only) shows similar values on every cylinder, with none standing out.

How to record the log

• Warm the engine: coolant at least 80 °C. The specified values in workshop tables apply from this temperature.
• Let it idle with the car standing still, and keep the load the same for the whole log, e.g. with the air conditioning off.
• Log group 013 for one to two minutes. On a PD engine add groups 018 and 023. VCDS logs up to three groups at a time.
• Do not drive while logging. The control behind group 013 is meant for idle, and off idle the values are not calculated or stay frozen.

Group 013: injection quantity deviation per cylinder

The group is called "Idle Stabilization" (German Leerlaufruheregelung, idle smoothness control). The unit is "mg/H" or "mg/str": milligrams of fuel per stroke.

The control unit watches how evenly the crankshaft speeds up after each combustion. If one cylinder gives less than the others, it injects more fuel into that cylinder, and less into a cylinder that gives more. Group 013 shows these corrections.

Specified values

Warm engine (coolant at least 80 °C), idle, from the Dieselschrauber workshop tables:

For older VE engines (1Z, AHU, AFN, AVG) the tables give no value. For later PD engines with EDC16 (BKC, BXE, BLS, BKD) we did not find a table. Ross-Tech quotes ±2.0 mg, and ±2.8 mg on some engines, as the VW specification.

Within the specification does not always mean perfect. Many mechanics treat values up to about ±1 mg as healthy and start looking when one cylinder goes beyond that, especially if the engine shakes.

How to read the sign

• Positive: the control unit adds fuel to this cylinder because it gives less than the others. Typical causes are a weaker injector, a worn cam lobe or rocker on a PD engine, or lower compression.
• Negative: the control unit takes fuel away because the cylinder gives more than the others, e.g. its injector delivers more.
• The sum is about zero. The corrections only even out the cylinders against each other, so one weak cylinder at +2.5 pushes the others below zero. Look for the cylinder that stands out the most, not for every value other than zero. VCDS can show a small non-zero sum because it samples the values too slowly.

Example from a 1.9 TDI ALH with a nozzle from another TDI engine in cylinder 1: +1.84, −0.61, −0.56, −0.64 mg. After new nozzles: +0.42, +0.33, −0.21, −0.45 mg.

Injector or cylinder?

Group 013 shows which cylinder is off, not why. The order of checks recommended on the Dieselschrauber forum:

1. On PD engines: camshaft and rockers. The unit injectors are driven by the camshaft, and a worn cam lobe or rocker roller looks like a bad injector. Ross-Tech lists a worn camshaft as one of the causes of fault code 17668.
2. Compression of all cylinders.
3. The injector itself.

Swap test: swap the injector of the suspect cylinder with a neighbouring one (on PD engines with new seals) and log group 013 again. If the deviation moves with the injector, the injector is faulty. If it stays on the same cylinder, the cause is the cylinder: cam, rocker or compression.

A case from the Dieselschrauber forum: a 1.9 TDI BKC with cylinder 2 at +2.56 mg on a warm engine and compression at 36 bar on all cylinders. After the unit injectors were swapped, the fault stayed on cylinder 2, so the next thing to check was the camshaft.

The corrections of every cylinder jump between about +2 and −2 mg? If the corrections of all cylinders oscillate sharply, also check the other causes of uneven running, among them a loose timing belt, water pump or idler pulley, the dual-mass flywheel and an unstable fuel supply, e.g. air in the fuel. This picture does not rule out a fault in the injection system, though.

How vaglogs judges group 013

vaglogs diagnostics averages each cylinder over the whole log, from at least 5 samples. It reports a cylinder from an average of 2.0 mg in either direction, and treats 3.0 mg or more as critical. These are our thresholds, not a factory standard: on VE engines they match the specified range, on PD engines (±2.8 mg) the warning comes a little before the limit. Because the whole log is averaged, record it at idle only.

Group 018: unit injector status (PD)

On PD engines group 018 shows the status of each unit injector at idle. The specified value is 0 in every field. Ross-Tech refers to this group when describing fault code 17669. Engines with a distributor pump (VE) do not have it.

A value other than 0 is a sum of flags:

The meanings come from an independent PD diagnostics page (sources at the end). The VW test procedure lists the same states in the same order. A value of 20 is 16 + 4: BIP out of specification and a small injection quantity.

128 on one cylinder means the control unit could not detect the beginning of injection (BIP) on it. Check group 023 and the wiring of that injector (below).

Group 023: switch time deviation (PD)

Fields 1–4 are called "Switch Time Deviat. Cylinder 1" to "Cylinder 4". VCDS shows no unit, and the VW procedure gives the values in microseconds.

A unit injector starts injecting when its solenoid valve closes fully. This moment is called BIP (Beginning of Injection Period). The control unit detects it from the valve current and corrects the next injection. Group 023 shows how far each cylinder is from the expected moment.

• Range: forum posts quote −100 to +100 as the VW specification. A 1.9 TDI BKC at idle showed −17, −25, −15, −8.
• One cylinder far from the others points to the solenoid valve of that injector or its wiring. The current used to detect BIP is below 0.0001 A, so any extra resistance in the cable matters. In one case from the Ross-Tech forum, cylinder 2 showed about +125 with intermittent fault codes, and its solenoid measured about 0.2 Ω more than the others. A new injector solved it.
• Every cylinder strongly negative: the valve closes earlier than expected. VW names air in the injector as a cause, and forum users point to fuel starvation. Start with the fuel filter and the fuel supply.

On engines with more than four cylinders, the next cylinders are in group 024.

Typical fault patterns

Fault codes

The other cylinders have the next numbers, e.g. 17672 (P1264) is the regulation range of cylinder 2 (N241) and 18075 (P1667) its electrical fault. According to the Dieselschrauber tables, 17669 ("limit exceeded") points to switching times that are too long or to contact resistance, and 17670 ("limit not reached") to switching times that are too short or to fuel starvation. The pairs for cylinders 2–4 go up to 17679.

Common rail TDI

On EDC17 control units (UDS) you pick named values in Adv. Meas. Values instead of groups.

• Names: e.g. "Deviation of injected fuel volume: cylinder 1" to "cylinder 4", read at idle on a warm engine. Some engines show "Fuel injection time deviation: cylinder 1" in microseconds instead.
• Range: the VW procedure has one, but we did not find the numbers published. Compare the cylinders with each other and look for the one that stands out. If a value is out of range, VW says to check the injector code adaptation and the compression.
• Injector code (IMA): after replacing an injector or the control unit, its correction code has to be entered in the control unit (7 characters on the 2.0 TDI, a 20-digit Delphi code on the 1.2 TDI). A code entered for the wrong cylinder also causes a rough idle. In one T6 case the codes did not match the injector positions, and the engine ran smoothly once they were corrected.
• Not always the injector: in another T6 case cylinder 4 showed −72 µs, and the cause was a cracked intake manifold.

vaglogs diagnostics judges these values when the log gives them in mg per stroke. Time deviations in microseconds are not judged.

Frequently asked questions

What value in group 013 means the injector is broken?

A value outside the specified range (±2.0 mg on VE engines, ±2.8 mg on PD) is a reason to look further. Up to about ±1 mg is a healthy result. The value alone does not prove that the injector is faulty: a cam, rocker or low compression look the same. The swap test tells you which it is.

Some of my values are negative. Is that a problem?

Not on its own. The corrections add up to about zero, so if one cylinder is positive, the others go negative. Look at the cylinder furthest from zero.

Group 018 shows 128. What does it mean?

"BIP not possible": the control unit could not detect the beginning of injection on that cylinder. Check group 023 and the wiring of that injector.

Can I log group 013 while driving?

No. The control works at idle and off idle the values are not calculated or stay frozen. Record the log at idle on a warm engine.

The engine shakes after a new injector on a common rail TDI. Why?

Check whether the code of the new injector was entered, and for the right cylinder. Without it the control unit corrects the injector with the old values.

Can this be checked automatically?

Yes. Upload the CSV file to vaglogs. The diagnostics average group 013 for every cylinder and show which cylinder is off and by how much.

Sources

• Dieselschrauber workshop tables: PD engines, VE engines, 3-cylinder PD, 5-cylinder VE
• Dieselschrauber: the sign and the sum of the corrections, order of checks, every cylinder jumping, BKC case with a swap, group 023 and fuel starvation, fault codes
• Ross-Tech forum: VW specification for group 013, group 023 case
• Ross-Tech Wiki: fault codes 17668, 17669, 18075 and P0263, injector codes on the 2.0 CR TDI
• VW self-study programme 209: TDI with unit injectors
• TDIClub: ALH case with nozzles
• Group 018 states: interpreting PD engine data, VW procedure (BLS)
• Common rail: VW procedure (CAYC), T6 forum: injector codes and intake manifold