Cat internal-combustion forklifts built by Mitsubishi Caterpillar Forklift America (the GP15N–GP35N and GC15N–GC35N series, roughly 2005 onward) use the Nissan K21 or K25 engine and show engine faults on the meter panel as an E-code: E-21, E-32, E-43 and so on. The same engine and control module appear in Mitsubishi FG/FGC-N trucks and Nissan/UniCarriers Platinum-series trucks, so the table below applies to all three badges.
If your truck is an electric Cat (EP or ET series, or the older 2EC/2EP), it uses a different controller and numeric code set. That family is not covered here; the codes below will not match.
How the codes show up
A current fault shows on the LCD meter panel as "E" and a two-digit number while the key is on. Most codes also switch on the engine warning lamp. Some faults put the truck in a reduced-power mode; a few (E-27, E-28, E-30) usually stop it.
The code clears itself once the underlying condition is gone and the key is cycled. A stored history stays in the ECM and is read with the dealer diagnostic tool or the panel's diagnostic mode. If a code returns immediately after the key cycle, the fault is still present; if it returns days later, it is intermittent and usually a connector or harness problem.
E-code table
| Code | System | What it means / where to look |
|---|---|---|
| E-03 | VCM communication | CAN bus fault between the vehicle control module and the ECM. Check power and ground at the VCM, ECM, and meter panel; look for a chafed or unplugged CAN harness. |
| E-04 | ECM communication | Same CAN bus, seen from the other side. Usually appears with E-03. Check the OBD/maintenance connector for corrosion. |
| E-05 | DCM communication | Display/meter module lost communication. CAN harness and meter panel connectors. |
| E-07 | CAN bus | General bus malfunction. Treat as E-03/E-04. |
| E-21 | Mass air flow sensor | Signal out of range. Broken wire or loose connector at the MAF on the intake tube is the usual cause; the sensor itself fails less often. |
| E-22 | Coolant temperature sensor | Two-wire sensor on the engine. Check resistance and the connector before replacing. |
| E-23 | Throttle position sensor | Confirm 5 V reference from the ECM to the throttle body and that the ETC relay is powered. Corrosion in the relay box is common on trucks washed regularly. |
| E-24 | Accelerator pedal sensor | Voltage out of range, often low at idle. After repair, perform the two "key learn" procedures or the code will return. |
| E-25 | O2 sensor | Signal circuit fault. Check the connector, then the sensor. |
| E-26 | O2 sensor heater | Heater circuit fault. Same checks as E-25; usually the sensor. |
| E-27 | Crankshaft position sensor | Long crank or no start. Confirm fuel pressure is correct first; if it is, test the sensor, its air gap, and the connector. |
| E-28 | Camshaft position sensor | Produces a no-start. Sensor or wiring. |
| E-29 | LPG fuel cut circuit | Inspect the main "C" relay and the fuel lock-off circuit. |
| E-30 | ECM circuit | Check the main chassis ground (clean, unpainted contact), ECM power and ground, and the emergency stop switch if the truck has one. Swap the ECM with a known-good truck to confirm before buying one. |
| E-31 | Electronic throttle control actuator | Actuator circuit fault. Inspect the ETC relay for corrosion or water intrusion. |
| E-32 | Coolant overheat, stage 1 | Coolant reached about 230°F. Radiator clogged with debris, low coolant, failed fan or belt, or an operator holding the inching pedal and loading the torque converter. |
| E-33 | Coolant overheat, stage 2 | About 275°F. Shut down and find the cooling fault before running the truck again. |
| E-34 | Ignition signal | No voltage at the ignition coil. Verify 12 V at the coil with the key on; if present and the fault stays, coil, plug, or ECM driver. |
| E-35 | LPG fuel injection circuit | High resistance or corrosion at the injector connectors, or a blown 5 A fuse on the injector holder assembly. |
| E-36 | LPG fuel pressure sensor | Broken wire or loose connection at the sensor. |
| E-38 | LPG vaporizer | Outlet pressure too high. Check the vaporizer/regulator. |
| E-40 | Oil pressure sensor | Monitored by the meter panel; may not show as a visible fault. |
| E-41 | Stop lamp switch | Brake switch out of adjustment. Adjust it even if the truck has no brake lights, and hold the pedal down while clearing the code. |
| E-42 | Air/fuel ratio, gasoline | Mixture pegged full rich or full lean. |
| E-43 | Air/fuel ratio, LPG | Mixture out of range on LPG. Check that LPG pressure is stable with the key on; then look at a dirty or restricted air filter, a stuck main LPG injector, or an intake leak. |
| E-44 | Atmospheric pressure sensor | Broken wire or loose connection. |
The three codes people search for most
E-43 (LPG air/fuel ratio) is the most common code on these trucks because it is downstream of several cheap parts. Work in this order: air filter (a dirty flame-retardant element on a Cat lifts the mixture rich), LPG tank valve and hose for a restriction, vaporizer outlet pressure, then the main injector. A long crank before the code appears points toward fuel pressure rather than the mixture sensors. See the E43 diagnostic walkthrough for the step-by-step.
E-32 (coolant overheat, stage 1) is a real temperature event, not a sensor code. Check the radiator fins first; on a Cat in a lumber yard or recycling facility the core is usually packed. Then coolant level, fan belt, fan clutch, and the thermostat. If the operator rides the inching pedal, the torque converter heats the transmission oil, which shares the cooler.
E-27 (crankshaft position sensor) shows as an extended crank or no-start. Verify fuel pressure before condemning the sensor, because a starving engine that eventually catches produces the same symptom. If fuel is right, measure the sensor and check its wiring for chafing where the harness passes the block.
Clearing a code
Fix the cause, cycle the key, and confirm the display is clear. Codes E-24 and E-41 have their own quirks: E-24 needs the accelerator "key learn" procedures after any pedal or sensor work, and E-41 needs the brake pedal held while the code is cleared. If the same code returns with nothing else changed, the fault is still present, not a stale memory.
Parts that fix these codes
The fast movers are the air filter (E-43), coolant temperature sensor (E-22), throttle body/TPS (E-23), O2 sensor (E-25/26), and crank sensor (E-27). Flat Earth Equipment stocks the Caterpillar 91B61-00912 flame-retardant air filter and the Mitsubishi 32K62-00300 fuel filter/water separator, plus Caterpillar forklift parts and Mitsubishi parts by part number. For sensors and ECM-side components, send the truck model, serial, and the E-code and we will match the part number.
For engine-side repairs, the Nissan K21 engine reference covers specifications and common wear items.
Frequently asked questions
Are Cat and Mitsubishi forklift codes the same? For IC trucks with the K21/K25 engine, yes. Both are built by Mitsubishi Caterpillar Forklift America on the same platform, and the ECM code set is identical. UniCarriers/Nissan Platinum-series trucks with the same engine share it as well.
Why does my code go away and come back? An intermittent code is almost always a connector or harness issue: corrosion in a relay box, a chafed wire, or a loose pin. Wiggle-test the harness with the key on and watch for the code to set.
Does E-43 mean the truck is unsafe to run? It means the mixture is out of range. The truck will usually run, but rich operation fouls the plugs and O2 sensor and raises CO in an enclosed building. Address it promptly.
What does the truck do on E-32? Stage-1 overheat typically derates the engine. Stage 2 (E-33) is a shut-down condition. Do not keep operating through either.
Can I read stored codes without the dealer tool? Current codes display on the meter panel with the key on. Stored history requires the dealer diagnostic software or the panel's service mode, which is described in the truck's service manual for your model.