The TU engine is distantly related to the older X-Type engine — sharing a similar overhead camshaft architecture, but the key differences are the belt driven camshaft (the X is chain driven), and that the TU is mounted in a conventional upright position with a separate, end-on mounted transmission and unequal length drive shafts.

Early versions of this engine suffered premature piston failure which were of a special fuel-saving low-friction design.

Symptoms were piston slap, especially with a cold engine, excessive oil consumption and exhaust smoke.

The introduction of Euro III led to the adoption of multi point injection, but power remained the same (although there was a small torque increase).

The later TU2 version with 100 PS (74 kW; 99 hp) was created in 1992 for the Peugeot 106 Rallye, with the adoption of a Magneti Marelli fuel injection system and a catalytic converter.

This version in the 106 Rallye uses the taller TU3 aluminium block, different con rod lengths and pistons.

[1] This engine has been one of the most used by the PSA Group, with applications in superminis, compacts and midsize cars, including a stint in competition use in the Citroën AX GT Cup and the Citroën AX GTI Cup, held in many European countries throughout the early 1990s in both circuit racing and rallying.

In its early years, it was available with either a single or double barrel carburettor, with fuel injection introduced in 1990 for the AX GTI and 106 XSi, capable of delivering 100 PS (74 kW; 99 hp) at 6600 rpm.

A DOHC 16-valve version of the 1360 cc TU3 with variable valve timing was introduced in 2004 with the Peugeot 206 Quiksilver Edition.

An indirect injection diesel with mechanical pump (Bosch or Lucas variants depending on model and year).