4HP20 Technical Information

The ZF 4HP20 is a four-speed automatic transmission for transverse engines and front-wheel drive, built by ZF in Saarbrücken from 1995 until about 2008. It is rated for 330 Nm of input torque, which is why PSA fitted it to its more powerful models - the petrol V6 engines, the 2.2 HDi diesels (later also the 2.0 HDi 136) and the 2.8 HDi in the Boxer and Jumper - while the smaller engines got PSA's own AL4. The same unit appears under other names: Renault calls it LM0, PSA uses the code 20HZxx, and in the Mercedes-Benz Vito and V-Class (W638) it was the only automatic on offer.

Control is electronic with adaptive shift programmes, and the torque converter has a lock-up clutch. In the workshop the 4HP20 is a trouble-free, durable transmission: in our experience most units pass 200,000 km without intervention, and a large share of the "failures" that arrive are cheap to put right. This page shows how to tell those apart from the faults that really need a repair.

The 4HP20 served the more powerful PSA, Renault and Fiat Group cars of the late 1990s and 2000s, as well as the first-generation Vito. Approximate years by model:

• Peugeot: 406 and 406 Coupé 3.0 V6 (1996-2004); 605 3.0 V6 24V (1997-1999); 607 3.0 V6 (2000-2004) and 2.2 HDi (2000-2006); 807 3.0 V6 (2002-2006); 407 2.0 HDi 136 (2004-2008) and 2.2 16V (2005-2008); Boxer 2.8 HDi (2002-2006)
• Citroën: XM 3.0 V6 24V (1997-2000); Xantia 3.0 V6 (1997-2001, not the Activa); C5 3.0 V6 (2001-2004), 2.2 HDi (2001-2006) and 2.0 HDi 136 (2004-2008); C8 3.0 V6 (2002-2006); Jumper 2.8 HDi (2002-2006)
• Renault (code LM0): Laguna I 3.0 V6 24V (1997-2001); Safrane 3.0 V6 24V (1998-2000); Espace III 3.0 V6 24V (1998-2002)
• Fiat, Lancia, Alfa Romeo: Ducato 2.8 JTD (2000-2006); Ulysse II and Lancia Phedra 3.0 V6 (2002-2005); Lancia Kappa 3.0 V6 (1998-2000); Alfa Romeo 166 2.5 and 3.0 V6 Sportronic (1998-2007)
• Mercedes-Benz: Vito and V-Class W638 (1996-2003), all automatic versions

Two things are often confused. First, the Peugeot 407 3.0 V6 never had the 4HP20 - it came with the six-speed Aisin AM6 from the start, and the AM6 replaced the 4HP20 in the 607 and C5 V6 from late 2004, later in the other models, and in 2008 in the 407 and C5 2.0 HDi. Second, the 4HP20 has nothing in common with the PSA / Renault AL4 / DP0, although both are four-speed units found in the same model ranges.

Identification: the plate on the gearbox carries a ZF number from the 1019 000 0xx series, and on PSA cars a 20HZxx code. The number matters because several internal parts (C brake, filter, position switch, gaskets) differ between versions.

Mechanically this is classic ZF of the period: two coupled planetary gear sets, two multi-plate clutches (B and E) and three brakes (C, D and F). There is no one-way clutch and no band brake - every gear is produced by exactly two elements:

The torque converter (254 mm) has a lock-up clutch that closes in 2nd, 3rd and 4th gear with a controlled slip of about 50 rpm. That saves fuel and reduces heat, but it also means the clutch is working almost all the time.

The hydraulics are controlled by six solenoids in the valve body: two on/off solenoids - MV1 for the two line-pressure levels and MV2 for clutch E - and four pressure regulators - EDS3 for converter lock-up, EDS4 for brakes C and D, EDS5 for brake F and EDS6 for clutch B. The Bosch control unit works with ten shift programmes: six adaptive, a snow programme, one for warm-up and two for thermal protection. On a fault the transmission drops into limp mode - only 3rd gear and reverse remain, engaged purely hydraulically, with a noticeable jolt when D or R is selected. This is the mode most owners describe as "the gearbox is broken".

The complaints about a 4HP20 repeat themselves, but the causes behind them differ enormously in cost. So diagnosis runs from cheap to expensive.

Typical symptoms:

Step 1 - the periphery. Some of the most common causes of limp mode are outside the transmission itself: the brake pedal switch, the position switch (selector position sensor) and the adjustment of its cable, the wiring loom connector on top of the gearbox, and overheated fluid. The tell-tale sign is a fault that comes and goes - often when cold or as the unit warms up - and clears after the next start. These repairs usually cost a fraction of a gearbox repair, yet they are regularly misdiagnosed as "a new gearbox".

Step 2 - the fluid. Dark fluid that smells burnt at more than 100,000 km explains a large share of harsh shifting. Check the level by the correct procedure (see the fluid section) and change the fluid before looking for a mechanical fault.

Step 3 - codes and live data. Codes such as P0741 (converter lock-up), P0730 (incorrect gear ratio) and P0780 point to slip. A simple test with a diagnostic tool: at a standstill with the brake applied, input (turbine) speed must drop to zero when D is selected - if the turbine keeps turning, the elements are slipping. From here the choice is between the torque converter, the pump and the valve body, described below.

The 4HP20 runs only on fluid to the LT 71141 specification (Esso / Mobil ATF LT 71141) or an approved ZF TE-ML 11B fluid such as ZF LifeguardFluid 5. For the Vito the Mercedes specification is sheet MB 236.11 - the same type of fluid. Universal ATFs and Dexron III are not suitable, no matter how often they are recommended online.

Service data:

The remaining 5 L sit in the converter and the cooler, so a gearbox with black fluid is cleaned up with two or three partial changes at short intervals, not with one.

There are two different level-check procedures depending on the version, and mixing them up is the classic mistake. Early units (up to about 1999) have a dipstick: fluid at about 80 °C, engine idling, selector in P or N after cycling through all positions. Later units have no dipstick but a level plug: engine idling with no electrical consumers switched on, selector in P; the plug is opened at 55 °C, a thin trickle must appear, and the plug is refitted when the temperature reaches 60 °C. Temperature is read with a diagnostic tool, and the unit is filled through the breather opening. This is the PSA procedure - on the Vito follow the Mercedes instructions.

The filter comes in two variants depending on the version of the gearbox: short pick-up tube (ZF 0501 315 184) for Peugeot, Citroën and Renault, and long pick-up tube (ZF 0501 315 183) for Mercedes, Fiat, Lancia, Alfa Romeo and some later PSA codes. Check the gearbox code before ordering.

The converter lock-up clutch is usually the first part to wear out - most often after 200,000 km, although there are cases from as little as 100,000 km. A worn friction lining slips and overheats: vibration at a steady speed, droning in 4th at low revs, jolts on lock-up and finally slip codes. The clutch is not replaced on its own - the converter is opened and rebuilt with a new friction wafer, hub and seals, or replaced with a new one. With this fault the answer is an overhaul with a new or rebuilt converter, not a fluid change.

The oil pump is the second critical assembly. A worn bush and hardened O-rings make pressure fall as the unit warms up: a whine when cold that fades, and loss of drive when hot. A leak from the pump seal is also a reason to check the converter and the bush - in our experience the seal itself is rarely the root cause. ZF supplies the pump only as a complete assembly (1019 210 025); oversize bushes are available in the aftermarket. There is also a known case where a missing centring ring between the converter and the crankshaft destroyed the pump housing - check for it on installation.

The valve body of the 4HP20 is a compact unit that carries the six solenoids, the temperature sensor and the input speed sensor, joined in one wiring loom that ends in a connector on the case. The EDS regulators work with small clearances and meter pressure continuously, so contaminated or burnt fluid wears their plungers and seats. The result is unstable line pressure: harsh shifts, slip during shifts and finally limp mode.

The valve body is cleaned and tested on a bench, the solenoids are replaced individually or as a set, and a badly worn unit is replaced with a rebuilt valve body on an exchange basis - the PSA / Renault and Mercedes versions differ. Whenever it is opened, the gasket and O-rings of the valve body are replaced, as is the cover gasket. After a valve body, solenoid or converter replacement, PSA prescribes an adaptation reset and a road test, otherwise the transmission shifts harshly until it has relearned its adaptations.

On the electrical side, check the position switch on the gearbox (different for PSA, Mercedes, Fiat and Renault) and the adjustment of its cable, the output speed sensor and the condition of the connector - corroded pins produce the same symptoms as a faulty valve body.

The clutch and brake packs of the 4HP20 are durable and rarely burn out on their own - they are usually ruined by slip from low pressure or from a worn converter. In an overhaul they are replaced according to their condition, with a friction disc kit and a steel plate kit or individually:

• clutches B and E share the same 178 mm, 30-tooth friction discs (E - 5 discs, B - 3) with steel plates of different thicknesses;
• brakes D and F share the same 169 mm, 40-tooth friction discs (D - 4, F - 3), plus a selective steel plate of 1.8 / 2.1 / 2.4 mm for D that sets the clearance;
• brake C - two variants depending on the gearbox code: a single-sided 214 mm, 24-tooth disc or two double-sided 197 mm, 30-tooth discs. This is where ordering mistakes happen most often.

The bonded pistons (according to the catalogues, those of brakes C, D and F; the E piston is aluminium) age with heat: hardened rubber means pressure loss and slip precisely when hot. On a unit that has run on burnt fluid the set of three pistons is mandatory, not optional.

The output gear bearings and the differential bearings are checked every time the unit is opened - a noise that rises with road speed is the signal to replace them. Sealing is done with a complete overhaul kit: pump seal, axle seals, sealing rings on the input shaft and rear cover, O-rings and the gasket between the housings, which differs for PSA / Renault (1019 322 055) and for Mercedes / Fiat / Lancia (1019 322 056).

MID Auto stocks the complete range of parts for the 4HP20: overhaul kits, friction discs and steel plates individually and in kits, bonded pistons, torque converter parts, oil pumps and seals, bearings, filters for both variants, valve body parts, position switches, Mobil ATF LT 71141 fluid and new OEM gearboxes. Every part is shown in its position on the interactive transmission map, and the links in this article open the specific products.

When ordering, send us the gearbox code (1019 000 0xx or 20HZxx) or the VIN of the vehicle - that is how we select the correct filter, housing gasket, position switch and C brake variant. When working on the converter or the pump, order the pump seal, the O-ring, the filter (if the gearbox will be opened) and the fluid together with them, so the car is not left waiting on the lift.

The ZF 4HP20 is one of the most reliable four-speed automatics of its generation: robust mechanics, simple hydraulic control and predictable weak points. With fluid changes at sensible intervals, a correct level check and a timely response to vibration at cruising speed, units with 250,000-300,000 km are, in our experience, not rare. Most "death sentences" passed on this transmission are in fact a brake pedal switch, a position switch or a connector - start there.

Author: Tsanko Doktorov, chief mechanic and technical director of MID Auto. More than 30 years of experience specialising exclusively in automatic transmissions, with dozens of certificates from seminars and training courses in the repair and remanufacturing of automatic transmissions, torque converters and valve bodies. The article is based on MID Auto workshop practice and on ZF and PSA technical documentation for the 4HP20.